Introduction

LimeSurvey uses Expression Script which lets LimeSurvey support more complex branching, assessments, validation, and tailoring. It replaces how LimeSurvey manages Replacements, Conditions, and Assessments on the back-end. It also speeds up processing considerably since it eliminates most run-time database reads. Expression Script was developed by Dr. Thomas White (TMSWhite).

Key definitions

Expression: Anything surrounded by curly braces:
- As long as there is no white space immediately after the opening brace or before the closing curly brace.
- The expression content is evaluated by EM, so it can contain mathematical formulas, functions, and complex string and date processing.
Tailoring: Sometimes called "piping". It is the process of conditionally modifying text:
- You have access to all 'replacement fields', participant data, and response data.
- You also have easier access to questions, answers, and their properties.
Relevance Equation: A new question attribute controlling question visibility:
- If there is a relevance equation, then the question is only shown if the relevance evaluates to true.
- Internally, all array_filter and array_filter_exclude commands become subquestion-level relevance.
SGQA (how variables were named in the past):
- Stands for Survey-Group-Question-Answer
- SGQA variable names look like 123X5X382X971, and may have subquestion suffixes.
- These variable names are specific to the underlying S/Q/G/A database codes, so they often need to be changed
Equation Question Type: A new question type that saves calculations or reports to the database:
- It is like a Boilerplate question, but its contents are saved to the database even if you set "Always Hide this Question".
Question Code: This is the preferred variable name for EM:
- This can be a descriptive name indicating the purpose of the question, making it easier to read complex logic.
- Valid question codes should NOT start with a number, so when using the question code to number your questions, simply use "q1", or "q1a" or "g1q2".
- This is what becomes the variable name if you export data to SPSS or R. So, if you do statistical analysis, you need to create only unique question codes.

Do I have to use Expression Script?

The short answer is "no". However, this heavily depends on the complexity of the survey you want to create.

For example, the Conditions editor covers some basic expressions that can be applied to the questions of your survey. However, the Conditions editor is limited. That is why the Expression Script is used - it expands the realm of customization possibilities.

Can I mix Conditions and Relevance equations?

Yes. You can use the Conditions editor for some questions and Relevance equations for others.

You cannot have both conditions and expressions set up in the same question! Once a condition is set up, it replaces whatever expression is written in the relevance equation field. Moreover, the Relevance equation field cannot any longer be manually edited.

Yet, there is a way to use both expressions and conditions within a question. As mentioned above, a condition replaces the relevance equation field. Once done, check what is the newly created equation and copy it in a text editor. Delete the newly created condition from the Conditions editor and then edit the question by adding the condition-based expressions from your text editor file alongside the rest of expressions you wish to use.

How should I choose between Conditions and Relevance?

Here is a list of the pros and cons of each style:

Style	Pros	Cons
Conditions	1. Nice GUI for creating simple conditions. 2. GUI well documented and understood by support team	1. Only supports simple comparisons and does not "AND" and "OR" conditions well. 2. Cascading conditions work erratically 3. Slow - database intensive -it can slow down long surveys. 4. Some reported problems with reloading conditions. 5. GUI doesn't scale well when there are dozens, hundreds, or thousands of questions. 6. It could be slow to convert paper-based surveys since it must use SGQA names. 7. Often need a programmer to custom-code logic needed for complex branching.
Relevance	1. Supports very complex logic, including 80+ functions and math/string operators. 2. Perfect support for cascading logic. 3. Fast - no extra database calls, supporting 1000+ question surveys. 4. No problems with reloading logic since it does not require SGQA codes. 5. Syntax-highlighting scales to 1000+ question surveys. 6. Easy and fast to use for groups wanting to computerize existing paper-based surveys. 7. It easily supports semi-structured interviews and epidemiological surveys without needing a programmer.	1. No GUI for simple conditions - it makes use of syntax-highlighting instead.

Note:

We recommend you to use whatever fits better your needs.
For a more detailed explanation of the EM features, click on the following link.

Getting Started

The best way to get started with the EM is to:

Install the latest stable version from https://www.limesurvey.org/en/download.
Import and explore some sample surveys.
Explore the use cases and how-tos, and the step-by-step examples.
Explore the EM documentation (this page)
- Unit Tests of Isolated Expressions (advanced)
  - shows examples of using all EM functions and operators, and the PHP and JavaScript results;
  - note there are few functions that generate different results in the PHP and JavaScript versions, so this page lets you plan your EM logic accordingly.

Terminology

These words are commonly used to describe the capabilities of the EM:

Relevance-based Branching - if a question is relevant, then ask it, otherwise don't (e.g., make it invisible and mark it as NULL in the database). You may find the Relevance fields in the question editor panel as well as in the question group editor panel. The later is used to apply a set of conditions to an entire group without having to copy the same condition to each question, and/or combine group and question-level conditional logic).
Tailoring - Once you know which questions should be asked, tailoring (sometimes called piping) specifies how the question should be asked. This lets you support not only simple substitution (like {TOKEN:FIRSTNAME}), but also conjugation of verbs and declination of nouns based upon the gender or number of your subjects. It also lets you change the message you deliver to a survey respondent based upon whether they answered (or how they answered) other questions.
Equations - EM adds a new question type called Equation which stores the result of an Expression. The equation results are computed and written to the database, even if you hide them on the page. Thus, they are used for hidden scoring calculations, navigation based upon complex equations, assessments, and reports that will be generated and stored within the database.

Relevance and Cascading Relevance

Every question type now has a Relevance option which controls whether the question is displayed or not. The EM processes each Relevance Equation in the order they appear in the survey. If the expression is true (or missing - to support legacy surveys), the question will be displayed. If it is not relevant, then the question will be hidden, and the value will be NULLed in the database. If there are no relevant questions in a group, the entire group will be skipped.

Moreover, if any of the variables within an expression is irrelevant, then the expression always evaluates to false. This enables Cascading Relevance so that you do not have to write very long Relevance equations for each question.

Say you have five questions Q1-Q5, and you only want to show Q2 if Q1 was answered, and Q3 if Q2 was answered, etc. The relevance equations might be:

Question Code	Relevance	Question
Q1	1	What is your name?
Q2	Q1	{Q1}, how old are you?
Q3	Q2	So, you are {Q2} years old. Are you married?
Q4	Q3 == "Y"	{Q1}, how long have you been married?
Q5	Q4	How many children do you have, {Q1}?

Group-level Relevance

ExpressionScript also supports group-level relevance. This makes it easier to implement looping. Say you want to collect information from up to 10 entities (such as products or people from a household), where you first determine how many entities need follow-up (such as by asking how many people live in a household or having people check which products they like from a long list). After knowing how many entities need follow-up, you can use Group-level relevance like {count >= 1}, {count >=2}, ... {count >= 10} for each of the 10 groups of follow-up questions. Within each group, you can have question-level conditional logic (e.g., gender or age-specific follow-up questions for each subject). The question and group-level relevance equations are ANDed together to determine which should be shown.

To check such an example, import the following survey: Census survey example.

It can be observed in the below screenshot that Person 1 group is displayed (or relevant) if the respondent lives with at least another cohabitant:

Tailoring/Piping

Anything within curly braces is now treated as an Expression (with one exception described below). Expressions have access to all the LimeReplacementFields and variables (via several aliases), all typical equation operators (mathematical, logical, and comparison), and to dozens of functions (that even work dynamically on the client-side).

By Using these equations, you can do things such as:

Conditionally show tailored messages to the respondents based on prior responses;
Create assessments and show assessment results (or conditionally branch or show messages) based upon those results, all without using the assessments module itself;
Conjugate verbs and decline nouns within questions, answers, and reports;
Show summaries of responses before the "Show your answers" page at the end of the survey.

Equations

There is a new question type called Equation. Think of it as a Text display question type, except that it stores the value of what is displayed in the database. So, if the Equation Question text contains an Assessment computation, that value would be stored in the database in a variable that can be displayed in public or private statistics.

Syntax

Anything contained within curly braces is now considered an Expression (with one exception: there must be no leading or trailing whitespace - this is needed to ensure the ExpressionScript does not try to process embedded JavaScript).

Note that it is OK for expressions to span multiple lines, as long as there is no whitespace after the opening curly brace or before the closing curly brace. This is especially helpful for nested "if()" statements like this:

{if(is_empty(PFTotals),
 '',
 if(PFTotals >= -5 && PFTotals <= -4,
   'Very Soft',
   if(PFTotals >= -3 && PFTotals <= -2,
     'Soft',
     if(PFTotals == -1,
       'Somewhat Soft',
       if(PFTotals == 0,
         'Moderate',
         if(PFTotals == 1,
           'Somewhat Hard',
           if(PFTotals >= 2 && PFTotals <= 3,
             'Hard',
             if(PFTotals >= 4 && PFTotals <= 5,
               'Very Hard',
               ''
             )
           )
         )
       )
     )
   )
 )
)}

The ExpressionScript supports the following syntax:

All standard mathematical operators (e.g. +,-,*,/,!);
All standard comparison operators (e.g. <,<=,==,!=,>,>=, plus their equivalents: lt, le, eq, ne, gt, ge);
Parentheses (so you can group sub-expressions);
Conditional operators (e.g. &&,| | and their equivalents: and, or);
Single and double-quoted strings (which can each embed strings with the other quote type);
Comma operator (so can have a list of expressions and just return the final result);
Assignment operator (=);
Pre-defined variables (to refer to questions, question attributes, and responses) - e.g., the SGQA codes;
Pre-defined functions (there are already 80+, and it is easy to add more).

Operators

EM syntax follows normal operator precedence:

Level	Operator(s)	Description
1	()	parentheses for grouping or calling functions
2	! - +	unary operators: not, negation, unary-plus
3	* /	times, divide
4	+ -	plus, minus
5	< <= > >= lt le gt ge	relative comparisons
6	== != eq ne	equality comparisons
7	and	logical AND
8	or	logical OR
9	=	assignment operator
10	,	comma operator

For consistency between JavaScript and PHP, the plus operator (+) does addition if both operands are numeric, but does concatenation if both parts are non-numeric strings. However, we recommend using the "join()" function for concatenation, as that makes your intent more clear. It also avoids unexpected results if you were expecting strings but got numbers instead (or vice versa).

Warning with mismatch number and string and alphabetical/numerical comparison

When you want to compare value with relative or equality comparisons, pay attention at mismatches. A value entered by user (or provided via answer code) can be used as number if it is clearly a number. If you surround one of the values with ", a text/string comparison will take place. If you want to compare as number, never surround a number with ".

For example Q0.NAOK > "50" is true if Q0.NAOK is a numeric question with 9 as value. This is because the operator > will assume it is an alphabetical comparison and not a numerical one.

To make sure that you compare integer values, you can use intval(Q0.NAOK) > 50. Just remember if Q0.NAOK is not a number (empty or a string), then intval(Q0.NAOK) === 0. To compare string values ("A" < "B") use strcmp directly : strcmp(Q0.NAOK,"B") or strcmp(Q0.NAOK,"A5").

Caution about using Assignment Operator (=)

You should avoid using the assignment operators unless absolutely necessary, since they may cause unexpected side-effects. For example, if you change the value of a previous response, the cascading relevance and validation logic between that question and the current question is not re-computed, so you could end up with internally inconsistent data (e.g., questions that stay answered but should have been NULLed, or questions that are skipped but should have been answered). In general, if you want to assign a value to a variable, you should create an Equation question type, and use an expression to set its value. However, there are some rare times that people really need this operator, so we made it available.

To help caution you about this operator, it is shown in red font within the syntax equations (so that you don't confuse it with "==").

Using assignment operator

The main reasons you may want to use the assignment operator are:

You need to set the default value via equation for a question that does not accept default values (such as list radio, where the user interface lets you pick one of the answer options, but does not let you enter an equation). However, be careful, as LimeSurvey will not be able to validate that your equation generates one of the allowable answers for that question;
You need to forcibly change the response to a previous question based upon a later response;
etc...

Attention : The assignment is done only in PHP. This means that the value is not getting updated on the same page, but only when the user moves to the next page. Therefore, please pay attention when the assignment operator is used on the same page with other expressions.

You can use all the expression manager system for this purpose. It's better to use an Equation for this purpose.

Some examples:

Set answer to a short text question in lowercase : {QCODE=strtolower(QCODE.NAOK)};
Set a default answer to an array question type at start of a survey : {Q1_SQ1=(is_empty(Q1_SQ1.NAOK),"A99",Q1_SQ1.NAOK)};
Set a default answer to an array texts question type at start of a survey : {Q1_SQY1_SQX1 = (is_empty(Q1_SQY1_SQX1.NAOK),"Inserted answer", Q1_SQY1_SQX1.NAOK)};
Set an answer with condition : {QCODE=if(YesNo="Y","A1","")}.

XSS security

With XSS enabled, some parts of the expression manager system cannot be used:

starting a HTML tag in expression but ending in another expression;
using a complex expression within a URL.

Please note that XSS is enabled by default in any LimeSurvey installation.

Examples and workarounds:

{if( 1 ,"","")}information{if( 1 ,"","")} is broken with XSS security, here you can use {if(1,"information","information")};
<a href="/script.php?value={if(QCODE == "Y","yes","no")}">next</a>, here you can use an equation question because using a complete question code is OK : <a href="/script.php?value={EQUATION.NAOK}">next</a>.

Access to variables

ExpressionScript provides read-only access to whichever variables you might need. For backwards compatibility, it provides access to the following:

TOKEN:xxx - the value of a TOKEN (e.g., TOKEN:FIRSTNAME, TOKEN:ATTRIBUTE_5) (only for not anonymous survey).
INSERTANS:SGQA - the display value of an answer (e.g., "Yes") - similar to using {QCODE.shown}.
All {XXX} values used by templates.
In question text, you can use {QID} replaced by the question id and {SGQ} replaced by the SGQA of the question.

In addition, ExpressionScript lets you refer to variables by the Question Code (the 'title' column in the questions table within the database). This is also the variable label used when you export your data to SPSS, R, or SAS. For example, if you have questions about name, age, and gender, you could call those variables name, age, and gender instead of 12345X13X22, 12345X13X23, and 12345X13X24. This makes equations easier for everyone to read and validate the logic, plus making it possible to shuffle questions around without having to keep track of group or question numbers.

Important: It is safer to refer to variables that occur in the preceding pages or questions.

Furthermore, ExpressionScript lets you access many properties of the question:

Syntax	Meaning	Example	Example Result
Qcode	an alias for Qcode.code	{implode(',',name,gender)}	'Tom','M'
Qcode.code	the selected response code for the question if it is relevant (otherwise blank), or the text value if it is not a coded question	{implode(',',name.code,gender.code)}	'Tom','M'
Qcode.NAOK	same as Qcode - see discussion of NAOK	{gender.NAOK}	'M'
Qcode.value	the assessment value for the question if it is relevant (otherwise blank), or the text value if it is not a coded question	{gender.value}	'1'
Qcode.valueNAOK	same as Qcode.value - see discussion about NAOK	{gender.valueNAOK}	'1'
Qcode.shown	the display value for the question	{implode(',',name.shown,gender.shown)}	'Tom','Male'
Qcode.question	the text of the question	{gender.question}	'What is your gender?'
Qcode.mandatory	whether the question is mandatory (Y/N)	{gender.mandatory}	'N'
Qcode.qid	the internal question number (not the sequential number)	{gender.qid}	337
Qcode.type	the question type	{gender.type}	'G'
Qcode.jsName	the correct javascript name for the question, regardless whether declared on or off this page	{gender.jsName}	'java1827X3X337'
Qcode.gid	the internal group number (not the sequential number)	{gender.gid}	3
Qcode.qseq	the sequential number of the question, starting from 0	{gender.qseq}	5
Qcode.gseq	the sequential number of the group, starting from 0	{gender.gseq}	1
Qcode.relevanceStatus	whether the question is currently relevant (0 or 1)	{gender.relevanceStatus}	1
Qcode.relevance	the question-level relevance equation	{gender.relevance}	'!is_empty(name)'
Qcode.grelevance	the group-level relevance equation	{gender.grelevance}	'num_children >= 5'
Qcode.sgqa	the SGQA value for this question	{gender.sgqa}	'1827X3X337'

HTML editor issue

If you use the HTML editor, some characters are replaced by HTML entities.

& by &
< by <
> by >

If you use HTML editor you need to use :

and for &
lt for <
le for <=
gt for >
ge for >=

It is recommended to clear your expression of HTML that appears within your expression. If you use the LimeSurvey HTML editor, click on the "Source" button (located in the upper left part of the editor) and delete all the characters that are not related to your expression (e.g.,

,
, and so on).

Qcode variable naming

Here are the details of how to construct a Qcode (and access some properties) by question type. In general, Qcodes are constructed as:

 QuestionCode . '_' . SubQuestionID . '_' . ScaleId

For comment and other, the corresponding question codes are QuestionCode_comment and QuestionCode_other, respectively.

Type	Description	Code	SubQs	Answer Options	Scales	Answer Code	Answer Shown	Relevance
5	5 Point Choice Radio-Buttons	Q1		1-5		{Q1}	{Q1.shown}	{Q1==3}
B	Array (10 Point Choice) Radio-Buttons	Q2	L1-L6	1-10		{Q2_L2}	{Q2_L2.shown}	{Q2_L2==7}
A	Array (5 Point Choice) Radio-Buttons	Q3	1-5	1-5		{Q3_1}	{Q3_1.shown}	{Q3_1>=3}
1	Array (Flexible Labels) Dual Scale	Q4	sq1-sq5	0:a1-a3	1:b1-b3	{Q4_sq1_0}	{Q4_sq1_1.shown}	{Q4_sq1_1=='b2'}
H	Array (Flexible) - Column Format	Q5	1-5	s,m,t		{Q5_1}	{Q5_1.shown}	{Q5_1=='s'}
F	Array (Flexible) - Row Format	Q6	F1-F5	1-5		{Q6_F3}	{Q6_F3.shown}	{Q6_F3==4}
E	Array (Increase/Same/Decrease) Radio-Buttons	Q7	1-7	I,S,D		{Q7_4}	{Q7_4.shown}	{Q7_4=='D'}
:	Array (Multi Flexi) 1 To 10	Q8	ls1,todo,ls2	min,max,avg		{Q8_ls1_max}	{Q8_ls2_avg.shown}	{Q8_ls2_min==7}
;	Array (Multi Flexi) Text	Q9	hp,st,sw	1st,2nd,3rd		{Q9_hp_3rd}	{Q9_hp_3rd.shown}	{Q9_hp_3rd=='Peter'}
C	Array (Yes/Uncertain/No) Radio-Buttons	Q10	1-5	Y,N,U		{Q10_1}	{Q10_1.shown}	{Q10_3=='Y'}
X	Boilerplate Question	Q11					{Q11.shown}
D	Date	Q12				{Q12}	{Q12.shown}
*	Equation	Q13				{Q13}	{Q13.shown}	{Q13>5}
~124~	File Upload (records number of files uploaded)	Q14				{Q14}		{Q14>0}
G	Gender Drop-Down List	Q15		M,F		{Q15}	{Q15.shown}	{Q15=='M'}
U	Huge Free Text	Q16				{Q16}	{Q16.shown}	{strlen(Q16)>100}
I	Language Question	Q17				{Q17}	{Q17.shown}	{Q17=='en'}
!	List - Dropdown	Q18		1-5		{Q18}	{Q18.shown}	{Q18==3}
L	List Drop-Down/Radio-Button List	Q19		A-Z		{Q19}	{Q19.shown}	{Q19=='X'}
O	List With Comment Drop-Down/Radio-Button List + Textarea	Q20		A-F		{Q20},{Q20comment}	{Q20.shown}	{Q20=='B'}
T	Long Free Text	Q21				{Q21}	{Q21.shown}	{strstr(Q21,'hello')>0}
M	Multiple Choice Checkbox	Q22	A-F, other			{Q22_E}, {Q22_other}	{Q22_E.shown}, {Q22_other.shown}	{Q22_E=='Y'}
P	Multiple Choice With Comments Checkbox + Text	Q23	A-F			{Q23_D}, {Q23_Dcomment}	{Q23_D.shown}	{!is_empty(Q23)}
K	Multiple Numerical Question	Q24	self,mom,dad			{Q24_self}	{Q24_self.shown}	{Q24_self>30}
Q	Multiple Short Text	Q25	A-F			{Q25_B}	{Q25_B.shown}	{substr(Q25_B,1,1)=='Q'}
N	Numerical Question Type	Q26				{Q26}	{Q26.shown}	{Q26 > 30}
R	Ranking Style	Q27	1-4			{Q27_1}	{Q27_1.shown}	{Q27_1==3}
S	Short Free Text	Q28				{Q28}	{Q28.shown}	{Q28=='mine'}
Y	Yes/No Radio-Buttons	Q29				{Q29}	{Q29.shown}	{Q29=='Y'}

Usage of NAOK

NAOK --> "Not Applicable" (NA) is alright (OK)

Using NAOK, means that all or some of the variables are irrelevant (e.g. "Not Applicable" (NA) is alright (OK)).

For example: count(Q1_SQ1,Q1_SQ2,Q1_SQ3,Q1_SQ4) give always an empty string if one subquestion of Q1 is filtered. To count the number of checked subquestion in such question can be count(Q1_SQ1.NAOK,Q1_SQ2.NAOK,Q1_SQ3.NAOK,Q1_SQ4.NAOK). If the subquestion is hidden, the EM returns an empty string.

Without NAOK, if one question or one subquestion is hidden, the EM returns always an empty string (same to returning false).

The .shown always use the NAOK system (empty string if hidden) but if you need the code of the answer: it's always a good idea to add .NAOK after the question code (except if you need it and know what you do).

More information is provided in the Overriding Cascading Conditions subsection.

The reserved "this", "self", and "that" variables

Quite often you want to evaluate all the parts of a question, such as counting how many subquestions have been answered or summing up the scores. Other times you want to process just certain rows or columns of a question (such as getting the row or column sums and storing them in the database). These reserved variables make that process relatively painless.

"This" variable

The "this" variable is used exclusively within the "Whole question validation equation" and "Subquestion validation equation" options (the later is not possible from GUI). It expands to the variable names of each of the cells within those questions. So, if you want to make sure that each entry is greater than three, you would set the "Subquestion validation equation" to (this > 3).

"Self" variable

The "self" and "that" variable are more powerful, and serve as macros which are expanded prior to processing equations. The syntax choices for the "self" variable are:

self
self.suffix
self.sub-selector
self.sub-selector.suffix

suffix is any of the normal qcode suffixes (e.g., NAOK, value, shown)

sub-selector can be one of the following:

comments - only subquestions that are comments (e.g., multiple choice with comment and list with comment);
nocomments - only subquestions that are not comments;
sq_X - where X is a row or column identifier. Only subquestions matching pattern X are selected. Note that search is done on complete code identifier, then sq_X match and include subquestions nX, X, Xn (e.g. if you use sq_1, subquestions a1, 1a, 1, 11 or 001 was included). Put attention at dual scale question type where subquestions code are QCODE_SQCODE_1 and QCODE_SQCODE_1 and to ranking question type where subquestions code are QCODE_1,QCODE_2 ....

Examples:

Has any part of a question been answered? -> {count(self.NAOK)>0}
What is the assessment score for this question? -> {sum(self.value)}

You can also use these to get row and column totals. Say you have an array of numbers with rows A-E and columns 1-5.

What is the grand total? -> {sum(self.NAOK)}
What is the total of row B? -> {sum(self.sq_B.NAOK)}
What is the total of column 3? -> {sum(self.sq_3.NAOK)}

"That" variable

The "that" variable is like the "self" variable, but it allows you to refer to other questions. Its syntax is:

that.qname
that.qname.suffix
that.qname.sub-selector
that.qname.sub-selector.suffix

qname is the question name without any subquestion extensions. So, let's create a question 'q1', 'q' representing also its qname.

Examples:

Has any part of question q1 been answered? -> {count(that.q1.NAOK)>0}
What is the assessment score for q2? -> {sum(that.q2.NAOK)}
What is the grand total of q3? -> {sum(that.q3.NAOK)}
What is the total of row C in q4? -> {sum(that.q4.sq_C.NAOK)}
What is the total of column 2 in q4? -> {sum(that.q4.sq_2.NAOK)}

The "self" and "that" variables can be used in any relevance, validation, or tailoring.

The one caveat is that when you use the Show logic file feature, it will show you the expanded value of "self" and "that". This lets you see the actual equation that will be generated so that you (and the EM) can validate whether the variables exist or not. This may seem confusing since you may see quite lengthy equations. However, if you edit the question, you will see the original equation using "self" and/or "that".

You should not use these variables if

you want to explicitly name each variable used in an equation, or
use variables that do not have subquestions (e.g., single response questions). In those cases, prefixing a variable with "that" is overkill, and you run the risk of getting unexpected results.

Access to functions

The ExpressionScript provides access to mathematical, string, and user-defined functions, as shown below. It has PHP and JavaScript equivalents for these functions so that they work identically on server-side (PHP) and client-side (JavaScript). It is easy to add new functions.

Implemented functions

The following functions are currently available:

Function	Meaning	Syntax
abs	Absolute value	number abs(number)
acos	Arc cosine	number acos(number)
addslashes	Quote string with slashes	string addslashes(string)
asin	Arc sine	number asin(number)
atan	Arc tangent	number atan(number)
atan2	Arc tangent of two variables	number atan2(number, number)
ceil	Round fractions up	number ceil(number)
checkdate	Returns true(1) if it is a valid date in gregorian calendar	bool checkdate(month,day,year)
convert_value	Convert a numerical value using a inputTable and outputTable of numerical values	number convert_value(fValue, iStrict, sTranslateFromList, sTranslateToList)
cos	Cosine	number cos(number)
count	count the number of answered (non-blank) questions in the list	number count(arg1, arg12, ..., argN)
countif	Count the number of answered questions in the list equal to the first argument	number countif(matches, arg1, arg2, ... argN)
countifop	Count the number of answered questions in the list which pass the criteria (arg op value)	number countifop(op, value, arg1, arg2, ... argN)
date	Format a local date/time	string date(format [, timestamp=time()])
exp	Calculates the exponent of e	number exp(number)
fixnum	Display numbers with comma as radix separator, if needed	string fixnum(number)
floor	Round fractions down	number floor(number)
gmdate	Format a GMT date/time	string gmdate(format [, timestamp=time()])
html_entity_decode	Convert all HTML entities to their applicable characters (always uses ENT_QUOTES and UTF-8)	string html_entity_decode(string)
htmlentities	Convert all applicable characters to HTML entities (always uses ENT_QUOTES and UTF-8)	string htmlentities(string)
expr_mgr_htmlspecialchars	Convert special characters to HTML entities (always uses ENT_QUOTES and UTF-8)	string htmlspecialchars(string)
expr_mgr_htmlspecialchars_decode	Convert special HTML entities back to characters (always uses ENT_QUOTES and UTF-8)	string htmlspecialchars_decode(string)
idate	Format a local time/date as integer	string idate(string [, timestamp=time()])
if	Excel-style if(test,result_if_true,result_if_false)	if(test,result_if_true,result_if_false)
implode	Join array elements with a string	string implode(glue,arg1,arg2,...,argN)
intval	Get the integer value of a variable	int intval(number [, base=10])
is_empty	Determine whether a variable is considered to be empty	bool is_empty(var)
is_float	Finds whether the type of a variable is float	bool is_float(var)
is_int	Find whether the type of a variable is integer	bool is_int(var)
is_nan	Finds whether a value is not a number	bool is_nan(var)
is_null	Finds whether a variable is NULL	bool is_null(var)
is_numeric	Finds whether a variable is a number or a numeric string	bool is_numeric(var)
is_string	Find whether the type of a variable is string	bool is_string(var)
join^{(New in 2.0 build 130129)}	Join elements as a new string	join(arg1, arg2, ... argN)
list	Return comma-separated list of non-blank values	string list(arg1, arg2, ... argN)
listifop^{(New in 3.16.1 )}	Return a 'glue'-separated list of the specified question property (retProp) from questions in the list which pass the criteria (cmpProp op value)	string listifop(cmpProp, op, value, retProp, glue, sgqa1, sgqa2, ... sgqaN)
ltrim	Strip whitespace (or other characters) from the beginning of a string	string ltrim(string [, charlist])
max	Find highest value	number max(arg1, arg2, ... argN)
min	Find lowest value	number min(arg1, arg2, ... argN)
mktime	Get UNIX timestamp for a date (each of the 6 arguments are optional)	number mktime([hour [, minute [, second [, month [, day [, year ]]]]]])
modulo-function	The modulo function is not supported yet. You can use the floor() function instead	floor(x/y)==(x/y)
nl2br	Inserts HTML line breaks before all newlines in a string	string nl2br(string)
number_format	Format a number with grouped thousands	string number_format(number)
pi	Get value of pi	number pi()
pow	Exponential expression	number pow(base, exp)
quoted_printable_decode	Convert a quoted-printable string to an 8 bit string	string quoted_printable_decode(string)
quoted_printable_encode	Convert a 8 bit string to a quoted-printable string	string quoted_printable_encode(string)
quotemeta	Quote meta characters	string quotemeta(string)
rand	Generate a random integer, see this example	int rand() OR int rand(min, max)
regexMatch	compare a string to a regular expression	bool regexMatch(pattern,input)
round	Rounds a number to an optional precision	number round(val [, precision])
rtrim	Strip whitespace (or other characters) from the end of a string	string rtrim(string [, charlist])
sin	Sine	number sin(arg)
sprintf	Return a formatted string	string sprintf(format, arg1, arg2, ... argN)
sqrt	Square root	number sqrt(arg)
stddev	Calculate the Sample Standard Deviation for the list of numbers	number stddev(arg1, arg2, ... argN)
str_pad	Pad a string to a certain length with another string	string str_pad(input, pad_length [, pad_string])
str_repeat	Repeat a string	string str_repeat(input, multiplier)
str_replace	Replace all occurrences of the search string with the replacement string	string str_replace(search, replace, subject)
strcasecmp	Binary safe case-insensitive string comparison	int strcasecmp(str1, str2)
strcmp	Binary safe string comparison	int strcmp(str1, str2)
strip_tags	Strip HTML and PHP tags from a string	string strip_tags(str, allowable_tags)
stripos	Find position of first occurrence of a case-insensitive unicode string (starting by 0, return false if not found)	int stripos(haystack, needle [, offset=0])
stripslashes	Un-quotes a quoted string	string stripslashes(string)
stristr	Case-insensitive strstr	string stristr(haystack, needle [, before_needle=false])
strlen	Get string length	int strlen(string)
strpos	Find position of first occurrence of an unicode string (starting by 0, return false if not found)	int strpos(haystack, needle [ offset=0])
strrev	Reverse a string	string strrev(string)
strstr	Find first occurrence of a string	string strstr(haystack, needle[, before_needle=false])
strtolower	Make a string lowercase	string strtolower(string)
strtotime	Parse about any English textual datetime description into a Unix timestamp	int strtotime(string)
strtoupper	Make a string uppercase	string strtoupper(string)
substr	Return part of an unicode string	string substr(string, start [, length])
sum	Calculate the sum of values in an array	number sum(arg1, arg2, ... argN)
sumifop	Sum the values of answered questions in the list which pass the criteria (arg op value)	number sumifop(op, value, arg1, arg2, ... argN)
tan	Tangent	number tan(arg)
time	Return current UNIX timestamp	number time()
trim	Strip whitespace (or other characters) from the beginning and end of a string	string trim(string [, charlist])
ucwords	Uppercase the first character of each word in a string	string ucwords(string)
unique	Returns true if all non-empty responses are unique	boolean unique(arg1, ..., argN)

Click here if you wish to find out more about planned (or being constrained) functions.

Create new expression functions with plugin ^{(New in 4.0.0 )}

If you need a new function that doesn't exist in core, you can create one with a plugin. Such a new function is created using the expressionManagerStart event.

ExpressionScript knows which variables are local

In order to properly build the JavaScript for a page, EM needs to know which variables are set on the page, and what their JavaScript ID is (e.g., for document.getElementById(x)). It must also know which variables are set on other pages (so that it can ensure that the needed <input type='hidden' value='x'> fields are present and populated).

Cascading Conditions

If any of the variables are irrelevant, the whole equation will be irrelevant (false). For example, in the following table, N/A means that one of the variables was not relevant:

Operator	Example	a	b	Result
+ (unary)	+a	N/A		false
!	!a	N/A		false
== (or eq)	a == b	N/A	5	false
== (or eq)	a == b	N/A	0	false
== (or eq)	a == b	N/A	N/A	false
!= (or ne)	a != b	N/A	5	false
!= (or ne)	a != b	N/A	N/A	false
!= (or ne)	a != b	N/A	0	false
> (or gt)	a > b	N/A	5	false
>= (or ge)	a >= b	N/A	5	false
< (or lt)	a < b	N/A	5	false
<= (or le)	a <= b	N/A	5	false
and	a and b	N/A	5	false
and	a and b	N/A	N/A	false
or	a or b	N/A	N/A	false
or	a or b	N/A	5	false
+	a + b	N/A	5	false
*	a * b	N/A	5	false
/	a / b	5	N/A	false
()	(a)	N/A		false
(exp)	(a && b)	N/A	5	false
(exp) op (exp)	(b + b) > (a && b)	N/A	5	false
function	sum(a,b,b)	N/A	5	false
function	max(a,b)	N/A	5	false
function	min(a,b)	N/A	5	false
function	implode(', ',a,b,a,b)	N/A	5	false
function	if(a,a,b)	N/A	5	false
function	is_empty(a)	N/A		false
function	is_empty(a)	0 (or blank)		true
function	!is_empty(a)	N/A		false

Overriding Cascading Conditions

Say you want to show a running total of all relevant answers. You might try to use the equation {sum(q1,q2,q3,...,qN)}. However, this gets translated internally to LEMif(LEManyNA("q1","q2","q3",...,"qN"),"",sum(LEMval("q1"),LEMval("q2"),LEMval("q3"),...,LEMval("qN"))). So, if any of the values q1-qN are irrelevant, the equation will always return false. In this case, the sum() will show "0" until all questions are answered.

To get around this, each variable can have a ".NAOK" suffix (meaning that Not Applicable is OK) added to it. In such cases, the following behavior occurs. Say you have a variable q1.NAOK:

q1 is not added to the LEManyNA() clause
LEMval('q1') will continue to check whether the response is relevant and will return "" if it is not (so individual irrelevant responses will be ignored, but they will not void the entire expression).

So, the solution to the running total problem is to use the equation sum(q1.NAOK,q2.NAOK,q3.NAOK,...,qN.NAOK).

The use of the .NAOK suffix also lets authors design surveys that have several possible paths but then converge on common paths later. For example, say subjects answer a survey in a way that is outside the normal range of responses. The author could alert the subjects that they may not get valid results, and ask them whether they really want to continue with the survey. If they say "Yes", then the rest of the questions will be shown. The condition for the "rest of the questions" would check whether the initial responses were answered within the normal range OR whether the subject said "Yes" to the question that is only relevant if they answered outside the normal range.

How does ExpressionScript support conditional micro-tailoring?

Here is an example of micro-tailoring (where Question Type=='expr' means an Equation):

Question Code	Relevance	Question Type	Question
name	1	text	What is your name?
age	1	text	How old are you?
badage	!is_empty(age)	expr	{(age<16) or (age>80)}
agestop	badage	message	Sorry, {name}, you are too {if( (age<16),'young',if( (age>80),'old','middle-aged') ) } for this test.
kids	!badage	yesno	Do you have children?
parents	1	expr	{!badage && kids=='Y'}
numKids	parents	text	How many children do you have?
kid1	parents && numKids >= 1	text	How old is your first child?
kid2	parents && numKids >= 2	text	How old is your second child?
kid3	parents && numKids >= 3	text	How old is your third child?
kid4	parents && numKids >= 4	text	How old is your fourth child?
kid5	parents && numKids >= 5	text	How old is your fifth child?
sumage	1	expr	{sum(kid1.NAOK,kid2.NAOK,kid3.NAOK,kid4.NAOK,kid5.NAOK)}
report	parents	text	{name}, you said you are {age} and that you have {numKids}. The sum of ages of your first {min(numKids,5)} kids is {sumage}

To download the above survey example, click on the following link: Number of kids survey example.

All of these questions can be on a single page (e.g., in the same group), and only the relevant questions will be displayed. Moreover, as you enter the ages of children, the sum() expression in the last question will dynamically get updated.

ExpressionScript provides this functionality by surrounding each expression with a named element. Every time a value changes, it recomputes the expression that should appear in that element and regenerates the display. You can have dozens or even hundreds of such tailored expressions on the same page.

Syntax highlighting

To help with entering and validating expressions, the EM provides syntax highlighting with the following features:

Types and Meanings of Syntax Highlighting

Color	Sample	Meaning	Tooltip	Comments
tan background	Sample	the whole equation	none	Anything within curly braces that is recognized as an equation (e.g., there is no leading or trailing whitepace) will be color-coded with a tan background to help distinguish it from surrounding text
bold red text	Sample	An error	Some explanation on error	Can be an unknow variable or an error in function. Survey is broken and the questions that rely on the respective expression will not be shown to the respondents.
blue text	Sample	function name	meaning and allowable syntax	It refers to function names or things that should be functions since they are followed by an open parenthesis. They are displayed in bold blue text. Tooltips show the meaning and allowable syntax for the function.
grey text	Sample	string	none	Single and double-quoted strings are shown in grey text.
cyan text	Sample	variable set on the same page,	[name or SGQA code]: question; value; answerList showing codes for each value	Any variable that is set on the same page as the question you are currently editing is shown in cyan text (it can be updated in javascript). The tooltip shows its name (if you used INSERTANS:xxx) or its SGQA code (if you used the new naming system), the actual question, and its current value (or blank if not set). If the question type expects responses from an enumerated value set, the mapping of the codes to display values is shown.
green text	Sample	variable set on a prior page	[name or SGQA code]: question; value; answerList showing codes for each value	Any variable that is set on a prior page is shown in bold green text. The tooltip shows its name (if you used INSERTANS:xxx) or SGQA code (if you used the new naming system), the actual question, and its current value (or blank if not set). If the question type expects responses from an enumerated value set, the mapping of the codes to display values is shown.
bold pink text	Sample	variable set on a later page ^{in general : empty at survey start, but can be filled with index or move previous}	[name or SGQA code]: question; value; answerList showing codes for each value	Any variable that is set on a prior page is shown in bold pink text. The tooltip shows its name (if you used INSERTANS:xxx) or SGQA code (if you used the new naming system), the actual question, and its current value (or blank if not set). If the question type expects responses from an enumerated value set, the mapping of the codes to display values is show.
bold tan text	Sample	a lime replacement value	the value	Lime Replacement Strings (like {TOKEN:xxx}, {PRIVACY_MESSAGE}) are shown in bold tan text.
red text	Sample	assignment operator (=)	warning message	If you use one of the assignment operator (=), that operator will be displayed in red text. This is meant to help prevent accidental re-assignment of values when you really meant to check whether a == b instead of setting the value of a = b.
normal black text	Sample	punctuation	none	All other punctuation signs within the expression are shown as normal black text.
red-boxed text	a bold red line surrounds the error	syntax error	description of the error	Any detected syntax errors are shown within red boxes. The tooltip shows the error. Examples include unmatched parentheses, use of undefined functions, passing the wrong number of arguments to functions, poorly structured expressions (e.g., missing operators between variables), trying to assign a new value to a read-only variable, trying to assign values to non-variables, or using unsupported syntax. Note that the syntax error dectection system may only report one error in an expression even if there are multiple errors; however, if any errors are detected, at least one error will be shown.

By tooltips, we refer to the popup message that is displayed when you hover over certain functions and variables.

ExpressionScript - Presentation

From LimeSurvey Manual