How to convert a simple array to an associative array?

Question

What is the fastest way to convert a simple array to an associative array in PHP so that values can be checked in the isset($array[$value])?

I.e. fastest way to do the following conversion:

$array = array(1, 2, 3, 4, 5);
$assoc = array();

foreach ($array as $i => $value) {
        $assoc[$value] = 1;
}

use in_array($value, $array) instead of isset($array[$value]) — TarranJones, Sep 30 '15 at 10:55

score 41 · Answer 1 · edited Jul 21 '16 at 14:20

41

Your code is the exact equivalent of:

$assoc = array_fill_keys(array(1, 2, 3, 4, 5), 1); // or
$assoc = array_fill_keys(range(1, 5), 1);

array_flip(), while it may work for your purpose, it's not the same.

PHP ref: array_fill_keys(), array_flip()

edited Jul 21 '16 at 14:20

Joan

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answered May 27 '11 at 14:31

Alix Axel

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How can I apply this for two dimensional array? Thanks! – Dat TT May 30 '17 at 08:26
You're right. The correct way is array_fill_keys(), This should be the selected answer. – wp student Jul 09 '17 at 09:01

score 22 · Answer 2 · answered Nov 20 '18 at 08:37

22

If anyone is still wondering how to do this, there is an easier solution for this by using the array_combine function.

$array = array(1, 2, 3, 4, 5);
$assoc = array_combine($array,$array);

answered Nov 20 '18 at 08:37

A.M.N.Bandara

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this will not work if two keys are the same! – Daniel Carrera Jul 20 '21 at 04:07
This works great!! Just make sure that every key in your "key array" is unique. Also, you can just call it on the variable name of your "values array". It will replace it with the new associative array. – José Rasmussen Sep 29 '22 at 11:08
Note, that if performance is important array_combine is slow, consider using in_array instead – csandreas1 Jan 07 '23 at 06:54

score 21 · Accepted Answer · edited Jun 20 '20 at 09:12

21

array_flip() is exactly doing that:

array_flip() returns an array in flip order, i.e. keys from trans become values and values from trans become keys.

Note that the values of trans need to be valid keys, i.e. they need to be either integer or string. A warning will be emitted if a value has the wrong type, and the key/value pair in question will not be flipped.

If a value has several occurrences, the latest key will be used as its values, and all others will be lost.

But apart from that, there is only one type of array in PHP. Even numerical ("simple", as you call it) arrays are associative.

edited Jun 20 '20 at 09:12

Community

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answered May 27 '11 at 14:08

Felix Kling

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array_flip will do it ...thanks.. but isset(array[5]) is not set but on an associative array isset(assoc_array[5]) is set...because the value is the key ...but in simple array the array index is the key ...am I missing something – user773755 May 27 '11 at 14:29
@Rome: You are mixing two things here. Every array is associative. Of course `$array[5]` is not set, because the keys go from `0` to `4`. You want an array where the keys go from `1` to `5` (or in other words, you want to set the values of the on array as keys of the other). But still, both arrays are associative. The keys of `$array` are just starting from `0` and continuous integers. – Felix Kling May 27 '11 at 14:33
note: array_fill_keys is some how faster than array_flip with my limited testing – user773755 Jun 01 '11 at 20:59

score 0 · Answer 4 · answered May 14 '18 at 13:02

0

Simply use this logic

$var1 = json_encode($arr1, JSON_FORCE_OBJECT);
$var1 = json_decode($var1);

where $arr1 is the array that has to be converted to associative array. This can be achieved by json_encode and the json_decode the same

answered May 14 '18 at 13:02

Thyagi

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score -1 · Answer 5 · answered Jul 18 '19 at 16:06

function simple_to_associative($array) {
    $new_array = [];
    $i = 0;
    $last_elem = end($array);
    $nr_elems = count($array);
    foreach ($array as $index=>$value) {
        if($i % 2 == 0 && $last_elem == $value) {
            $new_array[$value] = '';
        } elseif($i % 2 == 0) {
            $new_array[$value] = $array[$index + 1];
        }
        $i++;
    }
    return $new_array;
}

Would work on any simple array of unlimited elements.

How to convert a simple array to an associative array?

5 Answers5

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