Extract ids from multi-dimensional array - php

Question

I have an array of db records that I want to convert from this:
array(2) {
[0]=>
array(1) {
["ID"]=>
string(1) "2"
}
[1]=>
array(1) {
["ID"]=>
string(1) "3"
}
}
To this:
array(2) {
[0]=>
string(1) "2"
[1]=>
string(1) "3"
}
I'm looking for the fastest performing/easiest solution to this.
I couldn't find any PHP functions for this.

Answer 1

On PHP 5.5 or later, the simplest solution would be using PHP's built-in array_column() function.
$ids = array_column($arr, 'ID');

Answer 2

$bas = array();
foreach ($foo as $bar) {
$bas[] = $bar['ID'];
}
print_r($bas);
Where $foo would be you original array and $bas the one you want to convert it to.

Answer 3

I wrote simple test for finding best solution between those:
// foreach
foreach ($array as $element) { $result[] = $element['ID']; }
// array_map
array_map(function($element) { return $element['ID']; }, $array);
// array_push
foreach ($array as $element) { array_push($result, $element['ID']); }
Results:
Test name Repeats Result Performance
foreach 1000 0,009204 sec +0%
array_push 1000 0,015731 sec -70,915%
array_map 1000 0,024891 sec -170,437%
From time to time they are slightly different, but foreach is always the best with outstanding performance results. So, seems #campari answer must be best answer. But i did not tested #kba solution, cause i'm on PHP 5.4. I suspect that array_column algorithm will show superior results.
Test code here: link.

Answer 4

Your input data (enriched with other data-types, -for testing-) and assuming you are using recent PHP versions:
$input = array(
0=>
array(
"ID"=> "2"
),
1=>
array(
"ID"=> "3"
),
"iamnotanarray", 100, null
);
exemplary:
$out = array_map( function($el){ return #current($el);}, $input);
generally:
$out = array_combine(
array_keys($ret)
,array_map( function($el){ return #current($el);}, $ret)
)
output:
var_export($out);
array (
0 => '2',
1 => '3',
2 => NULL,
3 => NULL,
4 => NULL,
)
var_dump($out);
array(5) {
[0]=>
string(1) "2"
[1]=>
string(1) "3"
[2]=>
NULL
[3]=>
NULL
[4]=>
NULL
}
To filter potentially unwanted data types, you may use:
$out = array_filter($out, is_string);
var_dump($out);
array(2) {
[0]=>
string(1) "2"
[1]=>
string(1) "3"
}
I didn't time it (yet), but this is using PHP's native precompiled functions. Speed varies with the gcc compiler optimizations of your PHP executable.
Note: #current is dirty, not recommended and just used for brevity/readability. It would yield the same effect as is_array($el) ? current($el) : NULL;

Answer 5

Try this-
$newArr = array();
foreach($array as $a) // $array is original array
{
array_push($newArr, $a["ID"]);
}
print_r($newArr);