Initializing help system before first use

Using Dynamic Variables

Dynamic variables allow you to define calculations or operations once and reference them in multiple expressions.

This is implemented with the <vdl-var> element which defines a variable's name and its value. Once defined, the variable can be referenced throughout the rest of a VDL view. Variable names should be unique and can be either globally-scoped or scenario-scoped, depending on where you define them.

The following view illustrates how to create and use globally-scoped variables. 
<vdl version="4.1">
  <vdl-var name="title" 
           value="Portfolio Optimization risky share types"></vdl-var>
  <vdl-var name="rows" 
           value="=[0,1,2,3,4]"></vdl-var>
  <vdl-page>
    <vdl-section heading="=vars.title">
      <vdl-column vdl-repeat="=row in vars.rows" 
                  heading="=row" 
                  size="4">
        <p vdl-text="=scenario.entities.RISK.length &&
                      scenario.entities.RISK[row].value ?
                      scenario.entities.RISK[row].value :
                      '' "></p>
      </vdl-column>
    </vdl-section>
  </vdl-page>
</vdl>

Note the ternary guard expression assigned to the vdl-text attribute. Also note the position of the <vdl-var> elements - outside a <vdl-page> element - this is what gives them global scope.

This renders as:

Globally Scoped Dynamic Variables Rendered

Rendered Global Dynamic Variables

To use a dynamic variable - say, title - at the scenario scope, it needs to contain an attribute that identifies its parent scenario by index. The following, changed code snippet illustrates the principle: 
<vdl version="4.1
    <vdl-section>
      <vdl-column vdl-repeat="=s,i in scenarios">
        <vdl-var name="title" value="='Portfolio Optimization scenario: ' + s.props.name" scenario="=i"></vdl-var>
          <span vdl-text="=s.vars.title"></span>
      </vdl-column>
    </vdl-section>
  </vdl-page>
</vdl>
Above, the scenario index is captured in the <vdl-repeat> element as the loop variable i, which is then used as the scenario index for the <vdl-var> element. See Using Loops with Arrays and Sets for further details of vdl-repeat.
Parent Topic Using VDL Expressions

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