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.

See also: stackoverflow.com/questions/13766898 -- dealing with array_key substrings instead of entire array_keys. — dreftymac
– dreftymac, Commented Aug 24, 2019 at 22:52
See also: underscorejs.org/#pick and stackoverflow.com/a/40270589/42223 for how this relates to higher-order-functions — dreftymac
– dreftymac, Commented Aug 24, 2019 at 23:11

Maciej Lew · Accepted Answer · 2015-01-19 21:31:43Z

58

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, 2015 at 21:31

Maciej Lew

6556 silver badges6 bronze badges

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

3 Comments

Joel.O Over a year ago

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.

user151841 Over a year ago

@Joel.O you can add a bounty to the question, and award it.

Dylan Pierce Over a year ago

This should be an internal PHP Array function.

Pradeep Sanjaya · Accepted Answer · 2012-09-22 11:51:14Z

8

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) {
}

edited Sep 22, 2012 at 11:51

answered Sep 22, 2012 at 11:41

Pradeep Sanjaya

1,8461 gold badge15 silver badges24 bronze badges

1 Comment

Brad Kent Over a year ago

How is this the accepted answer? Simple fix as per @Maciej's answer: array_intersect_key($array1, array_flip($array4));

Nicolas Dermine · Accepted Answer · 2019-09-16 12:36:25Z

0

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

edited Sep 16, 2019 at 12:36

answered Mar 12, 2018 at 16:54

Nicolas Dermine

6485 silver badges8 bronze badges

1 Comment

dreftymac Over a year ago

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: stackoverflow.com/a/8403958/42223

matt · Accepted Answer · 2019-11-20 21:01:45Z

0

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

answered Nov 20, 2019 at 21:01

matt

4,7541 gold badge32 silver badges34 bronze badges

1 Comment

matt Over a year ago

Thank you, matt from the past.

Collectives™ on Stack Overflow

PHP array function that returns a subset for given keys

4 Answers 4

3 Comments

1 Comment

1 Comment

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

3 Comments

1 Comment

1 Comment

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related