Validating how many times a question value appears across panels

[danlevison]

@JaneSjs

Hi,

Is there a built-in way in SurveyJS to validate how many times a specific question value appears across all panels in a dynamic panel (or similar repeating structure)?

For example, given a dynamic panel with the same question repeated in each panel:

• Can SurveyJS validate that a value appears no more than N times across all panels?

I know keyName (or uniquePropertyName) can be used to prevent duplicate responses for a question inside a dynamic panel, but is there a way to use expression-based validation to determine how many times a specific question value appears across panels?

For example a validation expression like this:

"expression": "countInArray({question1}, 'question2', {panel.question2}) <= 2"

I’m mainly trying to understand whether this kind of cross-panel counting is supported by expressions.

Any guidance on recommended approaches would be appreciated.

Many thanks!

[JaneSjs]

Hi,
Use an expression validator on the Dynamic Panel together with the built-in countInArray function.

countInArray counts items in a Dynamic Panel, Dynamic Matrix, or Multi-Select Matrix array where a specified field matches optional filter conditions. Attach a validator to the panel dynamic question (not to the inner template question) so the rule runs against all panels at once.

How countInArray works

countInArray({panelDynamicQuestion}, 'innerQuestionName', optionalFilterExpression)

• First argument — the Dynamic Panel question reference (for example, {employees}).
• Second argument — the name of a question inside the panel template whose value you want to evaluate.
• Third argument (optional) — a Boolean expression evaluated per panel/row. Only panels that satisfy the filter are counted.

To limit how often a specific choice appears (for example, 'JavaScript' selected in no more than three panels), use the allof operator in the filter expression.

Survey JSON Schema

The example below limits the 'JavaScript' skill to at most three employee records:

{
  "pages": [
    {
      "name": "page1",
      "elements": [
        {
          "type": "paneldynamic",
          "name": "employees",
          "title": "Employees",
          "validators": [
            {
              "type": "expression",
              "text": "You can select 'JavaScript' in no more than 3 employee records.",
              "expression": "countInArray({employees}, 'skills', {skills} allof 'JavaScript') <= 3"
            }
          ],
          "templateElements": [
            {
              "type": "checkbox",
              "name": "skills",
              "title": "Select skills",
              "choices": [
                "JavaScript",
                "TypeScript",
                "React",
                "Angular",
                "Vue"
              ]
            }
          ],
          "panelCount": 1,
          "displayMode": "tab"
        }
      ]
    }
  ]
}

Change the comparison (<= 3) and the filter expression to match your limit and value.

countInArray also works with Dynamic Matrix and Multi-Select Matrix when you need the same kind of cross-row counting.

keyName vs expression validation

Approach	Use when
keyName on the Dynamic Panel	Each panel must have a unique value for one template question (duplicates are blocked entirely).
countInArray + expression validator	A value may repeat, but only up to N times (or you need a minimum count).

Learn More

• Conditional Logic — Built-in Functions (countInArray)
• Data Validation
• Dynamic Panel Model API (keyName, keyDuplicationError)
• Expressions in Dynamic Panel (example)