PHP array function that returns a subset for given keys

Question

I'm looking for an array function that does something like this:

$myArray = array(
  'apple'=>'red',
  'banana'=>'yellow',
  'lettuce'=>'green',
  'strawberry'=>'red',
  'tomato'=>'red'
);
$keys = array(
  'lettuce',
  'tomato'
);

$ret = sub_array($myArray, $keys);

where $ret is:

array(
  'lettuce'=>'green',
  'tomato'=>'red'
);

A have no problem in writing it down by myself, the thing is I would like to avoid foreach loop and adopt a built-in function or a combination of built-in functions. It seems to me like a general and common array operation - I'd be surprised if a loop is the only option.

Duplicate: http://stackoverflow.com/questions/3454993/get-a-subset-of-an-array-based-on-an-array-of-keys — David Hancock, Sep 22 '12 at 11:45
**See also:** https://stackoverflow.com/questions/13766898/ -- dealing with array_key substrings instead of entire array_keys. — dreftymac, Aug 24 '19 at 22:52
**See also:** https://underscorejs.org/#pick and https://stackoverflow.com/a/40270589/42223 for how this relates to `higher-order-functions` — dreftymac, Aug 24 '19 at 23:11

score 55 · Accepted Answer · answered Jan 19 '15 at 21:31

55

This works:

function sub_array(array $haystack, array $needle)
{
    return array_intersect_key($haystack, array_flip($needle));
}

$myArray = array(
    'apple'=>'red',
    'banana'=>'yellow',
    'lettuce'=>'green',
    'strawberry'=>'red',
    'tomato'=>'red'
);
$keys = array(
    'lettuce',
    'tomato'
);

$ret = sub_array($myArray, $keys);

var_dump($ret);

answered Jan 19 '15 at 21:31

Maciej Lew

626
6
5

1

array_flip saved my life. Thanks. – ssi-anik Mar 25 '16 at 00:13
3

Thanks. New to php and coming from R where subsetting is done in a breeze, I was slowly starting to pull my hairs out. This saved my scalp ;) If I could give you +10 I would, gladly. – Joel.O Sep 30 '16 at 14:49
@Joel.O you can add a bounty to the question, and award it. – user151841 Aug 16 '17 at 19:03
This should be an internal PHP Array function. – Dylan Pierce Jan 11 '19 at 22:25

Pradeep Sanjaya · Answer 2 · 2012-09-22T11:51:14.413

You can use array_intersect_key, but it uses second array with keys and values. It computes the intersection of arrays using keys for comparison

array_intersect_key

<?php
$array1 = array('blue'  => 1, 'red'  => 2, 'green'  => 3, 'purple' => 4);
$array2 = array('green' => 5, 'blue' => 6, 'yellow' => 7, 'cyan'   => 8);
$array3 = array('green' => '', 'blue' => '', 'yellow' => '', 'cyan' => '');
$array4 = array('green', 'blue', 'yellow', 'cyan');

var_dump(array_intersect_key($array1, $array2));
var_dump(array_intersect_key($array1, $array3));
var_dump(array_intersect_key($array1, $array4));
?>

The above example will output:

array(2) {
  ["blue"]=>
  int(1)
  ["green"]=>
  int(3)
}

array(2) {
  ["blue"]=>
  int(1)
  ["green"]=>
  int(3)
}

array(0) {
}

How is this the accepted answer? Simple fix as per @Maciej's answer: array_intersect_key($array1, array_flip($array4)); — Brad Kent, Jan 29 '16 at 05:26

Nicolas Dermine · Answer 3 · 2019-09-16T12:36:25.610

0

    $ret = array_filter($myArray, function ($key) use ($keys) {
        return in_array($key, $keys);
    }, ARRAY_FILTER_USE_KEY);

edited Sep 16 '19 at 12:36

answered Mar 12 '18 at 16:54

Nicolas Dermine

628
5
8

1

**Note:** This may not return the result you are expecting, because the `$keys` variable is external to the anonymous function. Please check the `use` keyword -- as described in this stackoverflow post: https://stackoverflow.com/a/8403958/42223 – dreftymac Aug 24 '19 at 22:44

score 0 · Answer 4 · answered Nov 20 '19 at 21:01

One-liner:

$subArray = array_intersect_key($items, array_fill_keys($keys, 1));

Example:

<?php
$items = [ 'product_id' => 1234, 'color' => 'green', 'qty' => 5, 'desc' => 'Shirt' ];
$keys = [ 'product_id', 'desc' ];
$subArray = array_intersect_key($items, array_fill_keys($keys, 1));
var_dump($subArray);

Produces:

array(2) {
  ["product_id"]=>
  int(1234)
  ["desc"]=>
  string(5) "Shirt"
}

Works with:

numerical keys,
associative arrays,
mixed arrays,
arrays with non-unique values

PHP array function that returns a subset for given keys

4 Answers4

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