PHP: Merge specified sub-arrays into new array?

Question

I'm working in PHP and I need a function that will merge user specified sub-arrays within a 2D array into a new array, e.g.

$arr = [
    "sub_1" => [ "a", "b" ],
    "sub_2" => [ "c", "d" ],
    "sub_3" => [ "e", "f" ],
    "sub_a" => [ 1, 2, 3 ],
    "sub_b" => [ 4, 5, 6 ],
    "sub_c" => [ 7, 8, 9 ]
];

merge_subs( $arr, [ "sub_1", "sub_2", "sub_3" ] );
// should return: [ "a", "b", "c", "d", "e", "f" ]

merge_subs( $arr, [ "sub_a", "sub_b", "sub_c" ] );
// should return: [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]

What is the most efficient way to go about this?

EDIT:

This is what I tried but it doesn't work so I am clearly doing something wrong.

function merge_subs( $arr, $subs ){
    $new = [];
    foreach( $subs as $sub ){
        array_push( $new, $arr[$sub] );
    }
    return array_merge( $new );
}

EDIT 2:

I realized I left out the ellipsis and now I have it working. At any rate, I want to know if there is a better way to accomplish this.

Well you show us the way you did it, then we can see if we can make it more efficient — RiggsFolly
– RiggsFolly, Commented Jun 22, 2021 at 16:18
Did you try a simple look through the PHP manual? You may have found array_merge() if you had! — RiggsFolly
– RiggsFolly, Commented Jun 22, 2021 at 16:22
If you need to know which array to process and the names of the sub arrays you want to merge. it would be simpler to do $x = array_merge($arr['sub_1'], $arr['sub_2'], $arr['sub_3']); print_r($x); — RiggsFolly
– RiggsFolly, Commented Jun 22, 2021 at 16:43

Lawrence Cherone · Accepted Answer · 2021-06-22 16:43:21Z

1

Your looking for $new = array_merge($new, $arr[$sub]);

<?php
$arr = [
    "sub_1" => [ "a", "b" ],
    "sub_2" => [ "c", "d" ],
    "sub_3" => [ "e", "f" ],
    "sub_a" => [ 1, 2, 3 ],
    "sub_b" => [ 4, 5, 6 ],
    "sub_c" => [ 7, 8, 9 ]
];

function merge_subs( $arr, $subs ){
    $new = [];
    foreach( $subs as $sub ){
        $new = array_merge($new, $arr[$sub]);
    }
    return $new;
}


print_r(merge_subs( $arr, [ "sub_1", "sub_2", "sub_3" ] ));
// should return: [ "a", "b", "c", "d", "e", "f" ]

print_r(merge_subs( $arr, [ "sub_a", "sub_b", "sub_c" ] ));

Result:

Array
(
    [0] => a
    [1] => b
    [2] => c
    [3] => d
    [4] => e
    [5] => f
)
Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
    [5] => 6
    [6] => 7
    [7] => 8
    [8] => 9
)

answered Jun 22, 2021 at 16:43

Lawrence Cherone

46.7k7 gold badges66 silver badges107 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

AbraCadaver · Accepted Answer · 2021-06-23 14:09:01Z

1

The accepted answer does what you want by taking an array of keys and looping, but why? Just specify the the keys you want to merge:

$result = array_merge($arr[ "sub_1"], $arr["sub_2"], $arr["sub_3"]);

More involved than looping, but for fun:

function merge_subs($array, $keys) {
    return array_merge(...array_values(array_intersect_key($array, array_flip($keys))));
}

Get the elements from $arr with the same $keys passed array_intersect_key
Get the values array_values
Merge them as you would in the first example unpacking with ...

edited Jun 23, 2021 at 14:09

answered Jun 22, 2021 at 16:50

AbraCadaver

79.2k7 gold badges75 silver badges91 bronze badges

2 Comments

Malkalypse Over a year ago

I specified that I needed a function, so that this can be performed as needed with any provided array and specified subarrays. Can you demonstrate a function that will do what I need and does not use looping?

Malkalypse Over a year ago

It's still another working option, always good to have!

Collectives™ on Stack Overflow

PHP: Merge specified sub-arrays into new array?

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related