Calculated variables are a powerful addition to the functionality of Survey Solutions: they are named computable expressions, which can be added to a questionnaire for convenience when operating with large and/or complex expressions. Variables can be used to simplify and improve the validation and enabling conditions. The values of variables can be substituted into the question text or into a static text to provide more informative, dynamic content.
Every variable has a name, a type and an expression.
The variable name should obey the requirements for variable names.
Calculated variables may be of the following types:
Booleanfor expressions that evaluate to true or false.Doublefor expressions of numeric type allowing for decimal values (e.g. 2.5, 3.42).Date/Timefor expressions that are date and/or time.Long Integerfor expressions that evaluate to integer values. Unlike the double type, this type will only allow for whole numbers (e.g. 2, 42, 7329)Stringfor expressions that evaluate to strings (text).
These types are standard C# types which are described in the corresponding C# documentation.
The expression that you specify should evaluate to the type of the variable that has been declared.
Attention!
null.Calculated variables are included to data export by default. If this is not
desirable, the questionnaire author can prevent this by declaring the variable
not exportable (by setting the Do not export checkbox).
Examples
Example 1: Define full name from first and last names.
We want to define a variable fullName that is a combination of a
person’s first name (question firstName) and a person’s last name
(question lastName). Here the variable would be a String type because
the variable will contain text.
We can write this shortly as:
string fullName = firstName + " " + lastName
elsewhere in the documentation, with the understanding that the variable type
(string) is selected in the dropdown type selector, the variable name
(fullName) is written into the corresponding field as shown above, and the
expression (firstName + " " + lastName) is written (without the equality sign)
in the expression field.
Example 2: Count missing assets.
We want to define a variable countMissingAssets to count the number of
household assets where yes or no has not yet been filled in for
categorical multi-select question (question hhAssets) that is in yes/no
mode. Here the variable type would be long because we expect
the number of items missing a response to be a whole number.
long countMissingAssets = hhAssets.Missing.Length
We can later use it in a static text to the interviewer that will tell them how many assets they have not filled out yet.
Example 3: Calculate number of children in the household.
We want to define variable numChildren to equal the number of records in
the Persons roster corresponding to persons who’s age is less than 18 years.
Here the type of the variable should be long because we expect the
number of children to be whole number.
long numChildren = Persons.Count(person => person.age < 18)