itemUniqByProperty — GTM Variable Template for Items

VARIABLES › ITEMS

itemUniqByProperty EXTENDED Items

Direct (.tpl) Apply (.tpl) Add to GTM

Removes duplicate objects from an array based on a property value. Keeps the first occurrence.

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When to Use This

GA4 Ecommerce

Build and transform ecommerce data structures for GA4 event tracking.

Filtering

Select or exclude items from collections based on criteria or predicates.

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Examples

Deduplicate by item_id▶ Try

INPUT

Items (Array of Objects): [{item_id: "A", price: 10}, {item_id: "B", price: 20}, {item_id: "A", price: 30}]
Property Name: item_id

OUTPUT

[{item_id: "A", price: 10}, {item_id: "B", price: 20}]

No duplicates▶ Try

INPUT

Items (Array of Objects): [{name: "Shirt", price: 10}, {name: "Hat", price: 20}]
Property Name: name

OUTPUT

[{name: "Shirt", price: 10}, {name: "Hat", price: 20}]

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Live Sandbox

This is what you'll see when you open this variable in Google Tag Manager. Hover the icons for details.

itemUniqByProperty

Read-Only Try Live

Items (Array of Objects)

💾 Array of objects to deduplicate.

Supported formats:
  ✓ Array

Property Name

💾 The property to check for uniqueness (e.g. item_id, item_name).

Supported formats:
  ✓ String

Input Setup

Input Function (optional)

⚙️ Optional pre-processing function applied to the input before internal logic (e.g., convert object to string, normalize case). Internal transformations such as case handling will still apply afterward.

Result Handling

Output Function (optional)

⚙️ Optional function to apply to the result before returning it (e.g., str => str + ' €', val => val !== undefined for boolean conversion). Useful for chaining transformations on the output.

Items (Array of Objects) array

💡 Type any text to see the result update live

🎯 Using special value — click input to type instead

Test with:

Falsy undefined null "" empty 0 false NaN

Truthy true 42 "hello" {} empty [] empty {a:1} [1,2,3]

Property Name string

🔗 Result Handling — Chain Variables

Chain apply-mode variables to the output. Each variable receives the result of the previous one.

itemUniqByProperty()

+ Chain another variable

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Related Variables

Same category: Items

→ itemAssignDefaults → itemFilterByProperty → itemMapProperty → itemOmit → itemSet → itemSplitProperty → pluckProperty → sumProductOfProperties → sumProperty → sumPropertyNested → ⚡ ITEMS › Transformer

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Under the Hood

📜 View Implementation Code

/**
 * Removes duplicate objects from an array based on a property value.
 * Keeps the first occurrence of each unique value.
 *
 * @param {Array} data.src - Array of objects to deduplicate.
 * @param {string} data.prp - The property to check for uniqueness.
 * @param {Function|string} [data.out] - Optional output handler.
 *
 * Direct-mode specific parameters:
 * @param {Function} [data.pre] - Optional pre-processor function to transform src before processing.
 *
 * @returns {Array} A new array with duplicates removed based on the specified property.
 *
 * @framework ggLowCodeGTMKit
 */
const getType = require('getType');

const itemUniqByProperty = function(items, property) {
    if (getType(items) !== 'array') return [];
    if (typeof property !== 'string') return items;

    const seen = {};
    const result = [];
    for (var i = 0; i < items.length; i++) {
        const item = items[i];
        if (item == null || typeof item !== 'object') continue;
        const key = item[property];
        const keyStr = typeof key === 'undefined' ? '__undefined__' : '' + key;
        if (!seen.hasOwnProperty(keyStr)) {
            seen[keyStr] = true;
            result.push(item);
        }
    }
    return result;
};

const safeFunction = fn => typeof fn === 'function' ? fn : x => x;
const out = safeFunction(data.out);

// ===============================================================================
// itemUniqByProperty - Direct mode
// ===============================================================================
const applyCast = (castFn, value) => safeFunction(castFn)(value);
const value = applyCast(data.pre, data.src);
return out(itemUniqByProperty(value, data.prp));

// ===============================================================================
// itemUniqByProperty(...) - Apply Mode
// ===============================================================================
/*
return function(value, property) {
   property = data.rp1 ? property : data.prp;
   return out(itemUniqByProperty(value, property));
};
*/

🧪 View Test Scenarios (7 tests)

✅ '[example] Deduplicate by item_id'
✅ '[example] No duplicates'
✅ All duplicates - keeps first only
✅ Empty array returns empty
✅ Null src returns empty array
✅ Items with missing property are kept (once)
✅ Numeric string coercion - treats 1 and 1-string as same