There are different ways to delete an array element, where some are more useful for some specific tasks than others.
Deleting a single array element
If you want to delete just one array element you can use unset()
or alternatively \array_splice()
.
If you know the value and don’t know the key to delete the element you can use \array_search()
to get the key. This only works if the element does not occur more than once, since \array_search
returns the first hit only.
Note that when you use unset()
the array keys won’t change. If you want to reindex the keys you can use \array_values()
after unset()
, which will convert all keys to numerically enumerated keys starting from 0.
Code:
$array = [0 => "a", 1 => "b", 2 => "c"];
unset($array[1]);
// ↑ Key which you want to delete
Output:
[
[0] => a
[2] => c
]
If you use \array_splice()
the keys will automatically be reindexed, but the associative keys won’t change — as opposed to \array_values()
, which will convert all keys to numerical keys.
\array_splice()
needs the offset, not the key, as the second parameter.
Code:
$array = [0 => "a", 1 => "b", 2 => "c"];
\array_splice($array, 1, 1);
// ↑ Offset which you want to delete
Output:
[
[0] => a
[1] => c
]
array_splice()
, same as unset()
, take the array by reference. You don’t assign the return values of those functions back to the array.
Deleting multiple array elements
If you want to delete multiple array elements and don’t want to call unset()
or \array_splice()
multiple times you can use the functions \array_diff()
or \array_diff_key()
depending on whether you know the values or the keys of the elements which you want to delete.
If you know the values of the array elements which you want to delete, then you can use \array_diff()
. As before with unset()
it won’t change the keys of the array.
Code:
$array = [0 => "a", 1 => "b", 2 => "c", 3 => "c"];
$array = \array_diff($array, ["a", "c"]);
// └────────┘
// Array values which you want to delete
Output:
[
[1] => b
]
If you know the keys of the elements which you want to delete, then you want to use \array_diff_key()
. You have to make sure you pass the keys as keys in the second parameter and not as values. Keys won’t reindex.
Code:
$array = [0 => "a", 1 => "b", 2 => "c"];
$array = \array_diff_key($array, [0 => "xy", "2" => "xy"]);
// ↑ ↑
// Array keys which you want to delete
Output:
[
[1] => b
]
If you want to use unset()
or \array_splice()
to delete multiple elements with the same value you can use \array_keys()
to get all the keys for a specific value and then delete all elements.
Depends on your priorities.
If performance is your absolute driving characteristic, then by all means use the fastest one. Just make sure you have a full understanding of the differences before you make a choice
- Unlike
serialize()
you need to add extra parameter to keep UTF-8 characters untouched: json_encode($array, JSON_UNESCAPED_UNICODE)
(otherwise it converts UTF-8 characters to Unicode escape sequences).
- JSON will have no memory of what the object's original class was (they are always restored as instances of stdClass).
- You can't leverage
__sleep()
and __wakeup()
with JSON
- By default, only public properties are serialized with JSON. (in
PHP>=5.4
you can implement JsonSerializable to change this behavior).
- JSON is more portable
And there's probably a few other differences I can't think of at the moment.
A simple speed test to compare the two
<?php
ini_set('display_errors', 1);
error_reporting(E_ALL);
// Make a big, honkin test array
// You may need to adjust this depth to avoid memory limit errors
$testArray = fillArray(0, 5);
// Time json encoding
$start = microtime(true);
json_encode($testArray);
$jsonTime = microtime(true) - $start;
echo "JSON encoded in $jsonTime seconds\n";
// Time serialization
$start = microtime(true);
serialize($testArray);
$serializeTime = microtime(true) - $start;
echo "PHP serialized in $serializeTime seconds\n";
// Compare them
if ($jsonTime < $serializeTime) {
printf("json_encode() was roughly %01.2f%% faster than serialize()\n", ($serializeTime / $jsonTime - 1) * 100);
}
else if ($serializeTime < $jsonTime ) {
printf("serialize() was roughly %01.2f%% faster than json_encode()\n", ($jsonTime / $serializeTime - 1) * 100);
} else {
echo "Impossible!\n";
}
function fillArray( $depth, $max ) {
static $seed;
if (is_null($seed)) {
$seed = array('a', 2, 'c', 4, 'e', 6, 'g', 8, 'i', 10);
}
if ($depth < $max) {
$node = array();
foreach ($seed as $key) {
$node[$key] = fillArray($depth + 1, $max);
}
return $node;
}
return 'empty';
}
Best Answer
In PHP you can do this using Reflections. To invoke protected or private methods use the setAccessible() method http://php.net/reflectionmethod.setaccessible (just set it to TRUE)