PHP array_filter to get only one value from an array [duplicate]

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

The array_filter() callback returns a true/false indicating whether the element should be included or excluded from the filtered array; you're always returning a truthy value — Mark Baker
– Mark Baker, Commented May 18, 2016 at 12:25
If you want to get just the ids (column 0), then you should be using array_column(): $ids == array_column($data, 0); — Mark Baker
– Mark Baker, Commented May 18, 2016 at 12:27
array_column works like a charm! And I believe it's exactly what I need in this case. — Ben
– Ben, Commented May 18, 2016 at 12:28
array_filter() is not working as intended and Manipulate array filter in php value array not change and Why doesn't array_filter() mutate my strings while it iterates? and problem in array_filter() and strlen function — mickmackusa
– mickmackusa ♦, Commented Dec 11, 2022 at 12:32

iainn · Accepted Answer · 2020-12-30 20:17:13Z

17

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.

edited Dec 30, 2020 at 20:17

answered May 18, 2016 at 12:25

iainn

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1 Comment

Ben Over a year ago

Thanks for clarifying the difference. Somehow filter sounds more logical to me. +1A

user6319567 · Accepted Answer · 2016-05-18 13:06:17Z

10

Try this code

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

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

answered May 18, 2016 at 13:06

user6319567

1 Comment

mickmackusa Over a year ago

This is the best answer, it's a shame that it is a code-only answer from a deleted user. This is exactly what array_column() is for.

Peter Chaula · Accepted Answer · 2016-05-18 12:36:07Z

2

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];
           })

answered May 18, 2016 at 12:36

Peter Chaula

3,7812 gold badges36 silver badges37 bronze badges

1 Comment

Ben Over a year ago

That looks more complicated than the suggested array_column or array_map. Thanks for the contribution to show array_walk's possibilities. +1

Richard · Accepted Answer · 2016-05-18 12:25:20Z

0

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"
  }
}

answered May 18, 2016 at 12:25

Richard

1,0557 silver badges11 bronze badges

Comments

Jignesh Patel · Accepted Answer · 2016-05-18 12:29:43Z

0

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);

answered May 18, 2016 at 12:29

Jignesh Patel

1,0226 silver badges10 bronze badges

1 Comment

Thamilhan Over a year ago

Check other answers before posting! It is already posted by @iainn

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