Complex Evaluations, Formulas and Functions

When customizing your surveys, you typically need a way to specify the following:

  1. Navigation/Branching - letting a subject's answers change the order in which questions are asked
  2. Tailoring/Piping - how to phrase the question (such as referring to prior answers, or conjugating sentences based upon the number or gender of your subjects), or how to generate custom reports (like assessment scores or tailored advice).
  3. Validation - ensuring that answers pass certain criteria, like min and max values, or matching an input pattern

Expression Manager (EM) provides an intuitive way to specifying the logic for each of those features.  Nearly anything that you can write as a standard mathematical equation is a valid expression, even if you are calling functions.  EM currently provides access to 70 functions, and can be easily extended to support more.  It also lets you access your variables using human-readable variable names (the question and answer codes).

Advanced Navigation/Branching Control

Some surveys use "Goto Logic", such that if you answer Question 1 with option C, then jump to Question 5. This approach is very limiting, since is hard to validate, and easily breaks when you have to re-order questions.  EM uses a Boolean relevance equation to specify all of the conditions under which a question might be valid.  If the question is relevant, then the question is shown, otherwise it is Not Applicable, and the value NULL (basically, "blank") is stored in the database. This is similar to what can be done via the Conditions editor (Set conditions), but EM lets you easily specify much more complex and powerful criteria using the question or answer code.

Functions You can Use 

The following functions are currently available (functions with links mean they are based on the PHP programming language -- and you can read more about functionality by following the link. 

In the syntax column the first word describes what data type is returned by the function (so in the first case, abs(number) will return a number/numeric value).

Note: Functions must be wrapped in curly braces ({ } like {abs(number)}

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 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)
log The logarithm of number to base, if given, or the natural logarithm. number log(number,base=e)
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 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)


Syntax follows normal operator precedence:

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


Access to Variables

EM provides read-only access to whichever variables we 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"). For Expression Manager it's the same that using {QCODE.shown}.
  • All {placeholder} 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, EM lets you refer to variables by the Question Code.  This is also the variable label used when you export your data to SPSS, R, or SAS.  This makes equations easy for everyone to read and validate the logic.

Important: It is only safe to refer to variables that occur in preceding pages or questions.

Furthermore, EM lets you access many properties of the Question:

SyntaxMeaningExampleExample Result
Qcode an alias for Qcode.code (see below) {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  - Using NAOK means that all or some of the variables are irrelevant (e.g. "Not Applicable" (NA) is alright (OK)). {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 Qcode.NAOK above  {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'


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