PHP Array Combine Function

The array_combine() function in PHP merges two flat arrays into one associative array: it takes the values of the first array as the keys and the values of the second array as the values. It is the go-to tool when you have two parallel arrays — for example, a list of column names and a list of cell values that line up position-by-position — and you want to zip them into a single key/value map.

This page covers the syntax, what each parameter and the return value mean, the rules you must follow (equal length, valid key types), and the most common real-world patterns.

Syntax

array_combine(array $keys, array $values): array

Return value: a new associative array built by pairing each element of $keys with the element of $values at the same position.

Since PHP 8.0, passing arrays of different sizes throws a ValueError. In PHP 7.x and earlier the function instead returned false and emitted a warning.

Basic usage

The classic use case is turning two parallel arrays into one map — here, product names paired with their prices.

This will output:

Array
(
    [Product 1] => 10
    [Product 2] => 20
    [Product 3] => 30
)

Combination is done by position, not by sorting or matching — the first key pairs with the first value, the second with the second, and so on.

Building a row from headers and data

A frequent practical use is reconstructing an associative record from a CSV-style header row plus a data row. This is exactly how you might map one line of a parsed CSV file.

<?php

$headers = array("id", "name", "email");
$row     = array(101, "Ann", "[email protected]");

$record = array_combine($headers, $row);

echo $record["name"] . " <" . $record["email"] . ">";

This outputs:

Ann <[email protected]>

Rules and gotchas

Keep these constraints in mind:

• Equal length is required. $keys and $values must have the same number of elements. On PHP 8+ a mismatch throws a ValueError; guard with count($keys) === count($values) if the lengths are not known in advance.
• Keys must be valid. Values used as keys must be integers or strings. Floats are truncated to integers, booleans are cast to 0/1, and null becomes the empty string "".
• Duplicate keys overwrite. If the $keys array contains repeated values, later pairs overwrite earlier ones, so the result can be shorter than the input. To get the unique key count first, see array_unique().
• Only the values are used. The original keys of both input arrays are ignored — only their values matter.

The example below shows a duplicate key collapsing two entries into one:

<?php

$keys   = array("a", "b", "a");
$values = array(1, 2, 3);

print_r(array_combine($keys, $values));

The last "a" => 3 overwrites the first, so the output is:

Array
(
    [a] => 3
    [b] => 2
)

Related functions

• array_merge() — joins arrays by appending values rather than pairing keys to values.
• array_flip() — swaps the keys and values of a single array.
• array_keys() and array_values() — the inverse operation: pull the keys or values back out of an associative array.

Conclusion

array_combine() is the cleanest way to zip two parallel arrays into an associative array, pairing them element-by-element. Remember the two rules that trip people up most: the arrays must be the same length (a ValueError on PHP 8+ otherwise), and duplicate keys silently overwrite each other.

Practice