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.

Answer 1

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); 

Answer 2

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) {
}