How to Create Custom Variables via QScript

This article describes how to create custom JavaScript and R variables using a QScript.

Requirements

• A Displayr Enterprise user license which includes the ability to add custom analysis menu items or use the Displayr API.
• The importdata.zip file which includes the Phone data set that we will use for this article.
• You have read How to Create a Custom QScript, How to Work with Variables via QScript, and How to Modify Variables and Value Attributes via QScript.
• This assumes you have also a regrouped variable set called Q5 as per the steps in the Combine section of How to Modify Variables and Value Attributes via QScript.
• You are using one of the methods from How to Use QScripts in Displayr.

Please note these steps require a Displayr license.

Method

Displayr has dedicated functions for creating JavaScript and R variables. Let's use a simple example where we wish to create a variable that identifies anyone who is under 25 based on our Age variable (q4).

Creating a JavaScript variable

To create this using a JavaScript variable, we would use the newJavaScriptVariable function:

project.dataFiles[0].newJavaScriptVariable("q4 < 4 ? 1 : 0", false, 
                                           "lessThan25", "Less than 25", null);

• We first tell it to add this new variable to our primary data set using project.dataFiles[0] and then set the newJavaScriptVariable arguments.
• We specify the condition q4 < 4 ? 1: 0 to return a 1 if q4 includes category values 1 through 3, i.e. less than 4, for all the ages under 25.
• We set the second argument to false as we wish to return a numeric variable. We would instead use true to return a text variable.
• We then specify the new variable name.
• Now we specify the new variable label.
• Finally, we set the position index. In this case, we will leave this as null to append the new variable to the top of the data set. You can, however, specify an exact row index.

Creating an R variable

To create this using an R variable, we would use the newRVariable function:

project.dataFiles[0].newRVariable('q4 %in% c("15 and under","16-19 years","20-24 years")', 
                                  "lessThan25", "Less than 25", null);

• We first tell it to add this new variable to our primary data set using project.dataFiles[0] and then set the newRVariable arguments.
• We specify the condition q4 %in% c("15 and under","16-19 years","20-24 years") to return a 1 if q4 includes these 3 category labels for all the ages under 25.
• We then specify the new variable name.
• Now we specify the new variable label.
• Finally, we set the position index. In this case, we will leave this as null to append the new variable to the top of the data set. You can, however, specify an exact row index.

Advanced examples

1. Creating a filter

Now let's look at a more advanced version of this example where we turn this new variable into a filter and perform additional validation and formatting functions:

// Add library
includeWeb('QScript Utility Functions');
// Set data file to add variable to
var data_file = project.dataFiles[0];
// Validate name/label
var var_label = preventDuplicateQuestionName(data_file, "Less than 25");
var var_name = preventDuplicateVariableName(data_file, "lessThan25");
// Set position of new variable
var position = data_file.getVariableByName('q4');
// Create new variable
var v = data_file.newJavaScriptVariable("q4 < 4 ? 1: 0", false, var_name, var_label, position);
// Set variable format
v.variableType = "Categorical";
v.valueAttributes.setLabel(0, "Not Selected");
v.valueAttributes.setLabel(1, "Selected"); 
v.question.isFilter = true;

• We use the preventDuplicateQuestionName and preventDuplicateVariableName functions from the QScript Utility Functions library to ensure there aren't already variables or variable sets with this name and label. Each variable and variable set needs to be unique in our data set, so these functions will append values to the name or label to ensure they can still be created without causing any conflict. By default, the functions will attempt to use the specified text.
• In order to have this new variable appear directly after our Age variable, we use getVariableByName and reference its variable name.
• We then pass the name and position arguments into newJavaScriptVariable. In this case, we have already declared our data file as data_file so can simplify this command.
• Finally, we set the variable type, add labels for each value, and set the variable as a filter.

2. Rebasing variables

The above examples create new variables without a code frame. However, there will be situations where you wish to recode a variable into another variable and copy the original code frame across or apply this to multiple variables.

The below example fits both criteria as it includes a custom function called rebaseVariableSet that we can use to create a rebased version of Q5 that removes any data for anyone under 25:

includeWeb('QScript Utility Functions');
includeWeb('QScript Value Attributes Functions');

function rebaseVariableSet(variable_set_name, condition) {
   var data_file = project.dataFiles[0];
   var q = data_file.getQuestionByName(variable_set_name);
   var q_vars = q.variables;
   var s = q.variableSetStructure;
   var is_text = s == "Text" || s == "Text - Multi";
   var rebased_vars = [];
   var last = q_vars[q_vars.length-1]; 
   // For each variable, create the appropriate rebased variable.
   for (var j=0; j<q_vars.length; j++) {
       var expression = "if (" + condition + ") "+ q_vars[j].name.toString() + ";\r\n else NaN";
       var new_v_name = preventDuplicateVariableName(data_file, q_vars[j].name.toString() + "rebased"); 
       var rebased_var = data_file.newJavaScriptVariable(expression, is_text, new_v_name ,q_vars[j].label.toString(), last);
       rebased_vars.push(rebased_var);
       last = rebased_var;
   }
   var new_q_name = preventDuplicateQuestionName(data_file, q.name + " - rebased");
   var new_variable_set = combineVariablesAsSet(new_q_name, s, rebased_vars);
   if (!is_text) 
      copyValueAttributesForQuestion(q, new_variable_set);
}

rebaseVariableSet("Q5","q4 > 3");

• We start by including references to the QScript Utility Functions and QScript Value Attributes Functions library so we can use some pre-built functions.
• Next, we build the function to include two arguments: variable_set_name and condition. The function declares the following JavaScript variables:
  • data_file is the document's data set.
  • q is the question object generated by using getQuestionByName with the function argument's variable_set_name argument.
  • q_vars stores all the variables from the question object.
  • s stores the Structure of the variable set.
  • is_text returns true or false if the Structure is text.
  • rebased_vars is set as an empty array.
  • last stores the index of the last variable.
  • We use a for…loop to iterate over each variable in our variable set using j as the index.
    
    • expression stores the function's condition argument to wrap within an if…else statement. The \r\n forces a line break in the code.
    • new_v_name is wrapped in preventDuplicateVariableName to ensure the variable name as a string with "rebased" appended doesn't already exist.
    • rebased_var uses newJavaScriptVariable to create the variable using the expression, text format, variable name, variable label, and position.
    • rebased_var is added to the empty rebased_vars array.
    • last is reset as the last index so when it loops through again it will add the next variable directly after the previous one.
  • new_q_name is wrapped in the preventDuplicateQuestionName function to ensure the variable set label with " - rebased" appended does not already exist.
  • new_variable_set uses the combineVariablesAsSet function to combine the rebased_vars variables using our updated variable set label and same data structure as the original.
  • If the Structure is not text, we use the copyValueAttributesForQuestion function to copy the variable and variable set characteristics of q over to new_variable_set.
• Finally, to use our rebaseVariableSet function with our example, we set Q5 as variable_set_name and q4 > 3 as condition.

Next

How to Add Pages, Folders, and Headings via QScript

Later

How to Create Tables and Calculations via QScript

How to Create a Visualization via QScript

How to Modify Tables via QScript

See Also

How to Work with Variables via QScript

How to Modify Variables and Value Attributes via QScript

How to Create a Custom QScript

How to Use QScripts in Displayr

JavaScript Fundamentals

How to Work with JavaScript Arrays and Loops