What exactly is the difference between array_map
, array_walk
and array_filter
. What I could see from documentation is that you could pass a callback function to perform an action on the supplied array. But I don't seem to find any particular difference between them.
Do they perform the same thing?
Can they be used interchangeably?
I would appreciate your help with illustrative example if they are different at all.
array_map
cannot change the values inside input array(s) while array_walk
can; in particular, array_map
never changes its arguments.array_map
cannot operate with the array keys, array_walk
can.array_map
returns a new array, array_walk
only returns true
. Hence, if you don't want to create an array as a result of traversing one array, you should use array_walk
.array_map
also can receive an arbitrary number of arrays and it can iterate over them in parallel, while array_walk
operates only on one.array_walk
can receive an extra arbitrary parameter to pass to the callback. This mostly irrelevant since PHP 5.3 (when anonymous functions were introduced).array_map
has the same length as that of the largest input array; array_walk
does not return an array but at the same time it cannot alter the number of elements of original array; array_filter
picks only a subset of the elements of the array according to a filtering function. It does preserve the keys.Example:
<pre>
<?php
$origarray1 = array(2.4, 2.6, 3.5);
$origarray2 = array(2.4, 2.6, 3.5);
print_r(array_map('floor', $origarray1)); // $origarray1 stays the same
// changes $origarray2
array_walk($origarray2, function (&$v, $k) { $v = floor($v); });
print_r($origarray2);
// this is a more proper use of array_walk
array_walk($origarray1, function ($v, $k) { echo "$k => $v", "\n"; });
// array_map accepts several arrays
print_r(
array_map(function ($a, $b) { return $a * $b; }, $origarray1, $origarray2)
);
// select only elements that are > 2.5
print_r(
array_filter($origarray1, function ($a) { return $a > 2.5; })
);
?>
</pre>
Result:
Array
(
[0] => 2
[1] => 2
[2] => 3
)
Array
(
[0] => 2
[1] => 2
[2] => 3
)
0 => 2.4
1 => 2.6
2 => 3.5
Array
(
[0] => 4.8
[1] => 5.2
[2] => 10.5
)
Array
(
[1] => 2.6
[2] => 3.5
)