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Table of Contents
How array_merge() works
How the operator works
Key differences summarized
Home Backend Development PHP Tutorial what is the difference between php array_merge and the operator

what is the difference between php array_merge and the operator

Jul 11, 2025 am 02:11 AM

The key difference between array_merge() and operators when merging arrays is the way keys are processed and values ??are overwritten. 1. array_merge() will re-index the numeric keys and retain the string keys. The key value of the same name in the subsequent array will overwrite the previous one; 2. The operator will retain all keys. When encountering key conflicts, the value of the left array is retained, and the value of the right array is ignored. Therefore, if you need to allow overrides and don't mind the number keys being rearranged, use array_merge(); if you need to keep the original key value and avoid overrides, use operators.

What is the difference between php array_merge and the operator

In PHP, both array_merge() and the operator are used to combine arrays, but they behave quite differently — especially when dealing with overlapping keys. Here's how they different and when you might want to use each one.

What is the difference between php array_merge and the operator

How array_merge() works

When you use array_merge() , PHP combines arrays and reindexes numeric keys starting from zero, while preserving string keys. If there are overlapping keys (especially string keys), the later array's value will overwrite the earlier one.

What is the difference between php array_merge and the operator

Example:

 $a = ['a' => 1, 'b' => 2];
$b = ['b' => 3, 'c' => 4];
$result = array_merge($a, $b);
// Results: ['a' => 1, 'b' => 3, 'c' => 4]
  • Numeric keys get reindexed.
  • String keys are preserved.
  • Duplicate string keys in later arrays replace earlier ones.

Use this when:

What is the difference between php array_merge and the operator
  • You want to merge arrays and allow overwriting of duplicate keys.
  • You're OK with numeric keys being renumbered.

How the operator works

The operator merges two or more arrays by preserving all keys , and if there's a key collision, the value from the leftmost array wins — meaning duplicates in the right-hand array are ignored.

Example:

 $a = ['a' => 1, 'b' => 2];
$b = ['b' => 3, 'c' => 4];
$result = $a $b;
// Results: ['a' => 1, 'b' => 2, 'c' => 4]
  • Keys are not reindexed (both numeric and string).
  • In case of key conflicts, the first occurrence is kept.
  • The order matters — left side takes priority.

Use this when:

  • You want to preserve all original values, even if there are duplicates.
  • You need to "fallback" data from another array without overriding existing keys.

Key differences summarized

Here's a quick breakdown:

  • Key handling:

    • array_merge() reindexes numeric keys and replaces duplicate string keys.
    • keeps all keys intact and retains the first encountered value for duplicates.
  • Overwrite behavior:

    • array_merge() lets newer values ??overwrite older ones.
    • sticks with the first value and ignores new ones.
  • Return type:

    • Both return a new array and don't modify the originals.

So depending on whether you care about preserving keys or allowing overwrites, you'll pick one or the other.

Basically that's it.

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