PHP: Combine two arrays keeping duplicate keys?

Question

How do I combine two arrays where the first array contains duplicate keys? e.g. combine the following:

$keys_arr
Array
    (
        [0] => iPhone
        [1] => iPhone
        [2] => iPhone
        [3] => Samsung
    )

$values_arr
Array
(
    [0] => 5
    [1] => 5
    [2] => 5
    [3] => Galaxy IV
)

The result I'm looking for is:

$combined_array
Array
    (
        [iPhone] => 5
        [iPhone] => 5
        [iPhone] => 5
        [Samsung] => Galaxy IV
    )

Using the following foreach (PHP - merge two arrays similar to array_combine, but with duplicate keys):

foreach ($keys_arr as $key => $value) {
    $combined_array[] = array($value => $values_arr[$key]);
}

I get:

Array
(
    [0] => Array
        (
            [iPhone] => 5
        )

    [1] => Array
        (
            [iPhone] => 5
        )

    [2] => Array
        (
            [iPhone] => 5
        )

    [3] => Array
        (
            [Samsung] => Galaxy IV
        )

)

Where am I going wrong?

The result you're looking for is not possible because PHP doesn't allow duplicate keys in an array — Mark Baker
– Mark Baker, Commented Feb 28, 2014 at 19:15
Why not try creating $combined_array = array(array('iPhone', '5'), array('iPhone' ,'5'), array('iPhone' ,'5'), array('Samsung' ,'Galaxy IV') ); — Mark Baker
– Mark Baker, Commented Feb 28, 2014 at 19:17
So it looks like you are combining two pieces of information about a single object together. You might consider combining to an array of objects like [{'product_line':'iPhone', 'model': '5'}, ... , {'product_line':'Samsung','model': 'Galaxy IV'}] such that you create a new property name for each of the array values by which you can definitively lookup the information you are trying to store. — Mike Brant
– Mike Brant, Commented Feb 28, 2014 at 19:19
$combined_array[] = ... will add a new element (which happens to be an array) to $combined_array. — gen_Eric
– gen_Eric, Commented Feb 28, 2014 at 19:25
@MarkBaker Thanks, I (stupidly) had no idea array keys had to be unique! — Elijah Paul
– Elijah Paul, Commented Feb 28, 2014 at 19:26

slava · Accepted Answer · 2016-02-11 08:39:45Z

0

php's associative arrays need to have unique keys for values - while you can have values that are all the same (i.e: 5, 5, 5), the keys MUST be distinct.

One way you can "work around" this is by using a Linked List data structure in the case of duplicates; this would result in;

$iPhone = {(5), (5), (5)}

$Samsung = Galaxy IV

An easy workaround to accomplish this would be to use a multi-dimensional array; i.e:

Array[iPhone] would hold a seperate array, containing {5, 5, 5}.

You can read up more on actual linked lists here; http://www.php.net/manual/en/class.spldoublylinkedlist.php

edited Feb 11, 2016 at 8:39

slava

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answered Feb 28, 2014 at 19:20

Eoghan

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