PHP INTERVIEW · Episode 04

What’s the difference between array_combine() and array_merge()?

Two very different ways to put arrays together

ep4_array_combine_and_merge.php

<?php
// Your code will go here.
$fruitsOne = ["Mangoe" , "Bananas" , "Orange"];
$fruitsTwo = ["Pineapple" , "Watermelon","Litchi"];

$mergedArray = array_merge($fruitsOne , $fruitsTwo);
$comoinedArray = array_combine($fruitsOne , $fruitsTwo);

Output

Output for this tutorial goes here.

Show the actual printed result of the code above.

Array merge output =

Array
(
    [0] => Mangoe
    [1] => Bananas
    [2] => Orange
    [3] => Pineapple
    [4] => Watermelon
    [5] => Litchi
)
        
         
            Array combine output =
           
Array
(
    [Mangoe] => Pineapple
    [Bananas] => Watermelon
    [Orange] => Litchi
)

The Question

Both functions build a new array out of existing ones, but they do completely different jobs. The names sound similar, which is exactly why interviewers like to ask.

array_merge()

array_merge() stacks arrays together into one. It appends the elements of each array onto the result.

Watch the keys: numeric keys are renumbered (0, 1, 2…), while for string keys a later value overwrites an earlier one with the same key.

array_combine()

array_combine() zips two arrays into one: the first array becomes the keys and the second becomes the values, paired by position.

Both arrays must have the same number of elements — if they don’t, PHP throws a ValueError (a warning/false before PHP 8).

Key takeaway: array_merge() = join arrays end‑to‑end (one long array). array_combine() = pair keys with values (a new associative array).

Tip: array_merge() is not the same as the + union operator — on a key clash, + keeps the first array’s value, while array_merge() keeps the last.

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