#PowerPlatformTip 24: 'Merge Arrays or Tables in Power Automate'

TL;DR: Merge two arrays and keep duplicates by joining each with a delimiter, concatenating, then splitting back, instead of union which drops duplicates.

💡 Challenge

You need to merge two arrays in Power Automate but keep the duplicates. The union function merges arrays, but it removes duplicates and returns only unique values.

🔀 Combine Two Arrays: union() vs. join/concat/split

There are two ways to combine (merge, join) two arrays in Power Automate – pick the one that matches your duplicate requirement:

Method	Expression	Duplicates
union()	union(outputs('array1'), outputs('array2'))	❌ removed
join → concat → split	split(concat(join(array1, '||'), '||', join(array2, '||')), '||')	✅ kept

There is no built-in merge() or combine() function – union() and the join/concat/split pattern below cover both cases.

✅ Solution

Instead of union, concatenate the arrays with a unique delimiter and then split the result back into an array. This preserves every element, including duplicates.

🔧 How It’s Done

1. Join each array into a string using a unique delimiter (||).

2. Concatenate both strings, keeping the delimiter between them.

3. Split the combined string back into an array using the same delimiter, all elements, duplicates included, are restored.

Here’s the expression:

split( concat( join(outputs('Compose_-_2_arrays')?['array1'], '||'), '||', join(outputs('Compose_-_2_arrays')?['array2'], '||') ), '||' )

🎉 Result

You merge both arrays while keeping all duplicate values, something the standard union function does not allow.

🌟 Key Advantages

🔸 Inclusivity: every element is kept, duplicates included.

🔸 Flexibility: adjust the formula for simple lists or more complex data structures.

🔸 Power: manipulate data in ways the standard functions don’t directly allow.

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🛠️ FAQ

1. How do I combine two arrays in Power Automate?

Use union(array1, array2) if duplicates may be removed, or the join/concat/split pattern above if every element must be kept.

2. How do I merge two arrays without removing duplicates?

union() always deduplicates. To keep duplicates use: split(concat(join(array1, '||'), '||', join(array2, '||')), '||').

**3. What happens if my array contains values that include the delimiter ‘

’?**

Choose a unique delimiter that doesn’t appear in your data, or use a more complex delimiter like ‘###DELIMITER###’.

4. Can this method handle arrays with different data types?

Yes, but ensure all values can be converted to strings for the join operation, then convert back to appropriate types if needed.

5. Is there a performance impact when merging large arrays?

For very large arrays, consider using the union() function for simple merging without duplicates, or batch processing for better performance.

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