PHP Splitting an Array into two arrays - keys array and values array

Is there an easy way to split an array into two arrays, one consisting of all the keys and the other consisting of all the values? This would be a reverse to the action of array_combine. Is there an inbuilt function for doing such a task? Let's use an example array:

$array = array('Tiger' => 'Forest', 'Hippo' => 'River', 'Bird' => 'Sky');

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Is there a function that will split the above array into:

$array_keys = array('Tiger', 'Hippo', 'Bird');
$array_values = array('Forest', 'River', 'Sky');

---

There are two functions called array_keys and array_values:

$array_keys = array_keys($array);
$array_values = array_values($array);

---

There are two functions actually:

$keys = array_keys($array);
$values = array_values($array);

You can also do the exact opposite:

$array = array_combine($keys, $values);

---

use array_keys and array_values

---

Strangely enough, the functions you're looking for are called array_keys() and array_values().

$keys = array_keys($array);
$vals = array_values($array);

---

Unfortunately there is no built-in inverse of array_combine. There is also no way to define one, since array_combine expects multiple parameters and we can't return multiple values from a function.

We can construct an alternative to array_combine which takes a single argument: the array of keys and the array of values wrapped up together in another array. This transformation is called "uncurrying" and is performed by the "call_user_func_array" function:

$array_comb  = function($arr) { return call_user_func_array('array_combine', $arr); };

This alternative function does have an inverse:

$array_split = function($arr) { return array(array_keys($arr), array_values($arr)); };

If we define function composition:

$compose  = function($f, $g) {
    return function($x) use ($f, $g) { return $f($g($x)); };
};

Then the following functions are all (extensionally) equal, ie. they all return their argument unchanged:

$identity      = function($x) { return $x; };
$left_inverse  = $compose($array_split, $array_comb);  // Split then combine
$right_inverse = $compose($array_comb, $array_split);  // Combine then split

Note that they accept different argument types though:

• $identity will work on anything.
• $left_inverse will work on any array.
• $right_inverse will work on arrays-of-arrays, where the outer array contains 2 elements, both inner arrays are of equal length and the first inner array only contains integers and strings.

---

function array_split($data)
{
  $x = 0;//Counter to ensure accuracy
  $retArray[0] = array();//Array of Keys
  $retArray[1] = array();//Array of Values

  foreach($data as $key => $value)
  {
    $retArray[0][$x] = $key;
    $retArray[1][$x] = $value;
    $x++;
  }

  RETURN $retArray;
}

$data = array("key" => "value", "key2" => "value2");

$splitData = array_split($data);

//print_r($splitData[0]);//Output: Array ( [0] => key [1] => key2 ) 
//print_r($splitData[1]);//Output: Array ( [0] => value [1] => value2 ) 

print_r($splitData);
//Output:
/*
Array
(
    [0] => Array
        (
            [0] => key
            [1] => key2
        )

    [1] => Array
        (
            [0] => value
            [1] => value2
        )

)
*/