PHP array_filter to get only one value from an array

Question

I'm trying to exclude foreach-loops and refactor them with array functions. I was under the assumption the code below would give me a result with all first items from the source array.

<?php
    $data= [
        0 => [1, 'test1'],
        1 => [2, 'test2'],
        2 => [3, 'test3'],
    ];

    $ids = array_filter($data, function($item) {
        return $item[0];
    });

    var_dump($ids);

But when I var_dump $ids I get the output:

array (size=3)
  0 => 
    array (size=2)
      0 => int 1
      1 => string 'test1' (length=5)
  1 => 
    array (size=2)
      0 => int 2
      1 => string 'test2' (length=5)
  2 => 
    array (size=2)
      0 => int 3
      1 => string 'test3' (length=5)

Why isn't the output:

array (size=3)
  0 => int 1
  1 => int 2
  2 => int 3

Answer 1

array_filter is used for filtering out elements of an array based on whether they satisfy a certain criterion. So you create a function that returns true or false, and test each element of the array against it. Your function will always return true, since every array has a first element in it, so the array is unchanged.

What you're looking for is array_map , which operates on each element in an array by running the callback over it.

<?php
$data= [
    0 => [1, 'test1'],
    1 => [2, 'test2'],
    2 => [3, 'test3'],
];

$ids = array_map(function($item) {
    return $item[0];
}, $data);

var_dump($ids);

As another answer mentions, if all you want to do is extract a single "column", then array_column is a much simpler option.

Answer 2

Try this code

$data= [
        0 => [1, 'test1'],
        1 => [2, 'test2'],
        2 => [3, 'test3'],
    ];

    $ids = array_column($data, 0);
    var_dump($ids);

Answer 3

The filter function needs to return a boolean(or any value that can be coerced to true) for each item so that it can be spared. So in your case it is always returning true for every element in the array

To get the result you 'd have to array_walk;

 $data = [
        0 => [1, 'test1'],
        1 => [2, 'test2'],
        2 => [3, 'test3'],
     ];


 array_walk($data, function($value, $key) use ($data){
                  $data[$key] = $value[0];
           })

Answer 4

the function included in the array_filter must return either true or false. 0 or empty array are converted to FALSE. Non-zero numbers are considered as true.

so if you want to find an item with id 2, you should compare it with 2 like this

<?php
$data= [
    0 => [1, 'test1'],
    1 => [2, 'test2'],
    2 => [3, 'test3'],
];

$ids = array_filter($data, function($item) {
    return $item[0] == 2;
});

var_dump($ids);

output

array(1) {
  [1] =>
  array(2) {
    [0] =>
    int(2)
    [1] =>
    string(5) "test2"
  }
}

Answer 5

Try below code

$data= [
        0 => [1, 'test1'],
        1 => [2, 'test2'],
        2 => [3, 'test3'],
    ];

    $ids = array_map(function($item) {
        return $item[0];
    }, $data);

    var_dump($ids);