array_filter
The previous post by [omnibus at omnibus dot edu dot pl] is not true, array_flip does work well with non-associative arrays.
I tested it in PHP v5.3.5.
array_flip
(PHP 4, PHP 5)
array_flip — Intercambia todas las keys con sus valores asociados en un array
Descripción
array array_flip
( array $trans
)
array_flip() retorna un array en orden volteado, es decir, las keys de trans se convierten en valores y los valores de trans se convierten en keys.
Se debe tener en cuenta que los valores de trans necesitan ser keys válidas, es decir, que necesitan ser entre un integer o un string. Una advertencia será emitida si un valor tiene el tipo erróneo y el par clave/valor en cuestión no será volteado
Si un valor tiene varias ocurrencias, la última key será usada como su valor y todos los demás se perderán.
Parámetros
- trans
-
Un array de pares key/valor para ser volteados.
Valores devueltos
Retorna el array volteado si es exitosa y NULL si falla.
Ejemplos
Example #1 Ejemplo de array_flip()
<?php
$trans = array_flip($trans);
$original = strtr($str, $trans);
?>
Example #2 Ejemplo de array_flip() : collision
<?php
$trans = array("a" => 1, "b" => 1, "c" => 2);
$trans = array_flip($trans);
print_r($trans);
?>
ahora $trans es:
Array
(
[1] => b
[2] => c
)
Ver también
- array_values() - Devuelve todos los valores de un array
- array_keys() - Devuelve todas las claves de un array o un subconjunto de claves de un array
- array_reverse() - Devuelve un array con los elementos en orden inverso
add a note
User Contributed Notes
array_flip
imikay at gmail dot com
22-May-2011 08:42
omnibus at omnibus dot edu dot pl
14-May-2011 05:31
Note that array_flip() does not work well with a non-associative array containing integers. I thought that array(0=>1, 1=>2), built without explicit definition of keys (defined like: $array[] = 1; $array[] = 2;), will be flipped to array(1=>0, 2=>1). Instead, I received some warnings.
h3x
12-Sep-2010 08:11
this function can be used to remove null elements form an array:
<?php
$ar = array(null,'1','2',null,'3',null);
print_r($ar);
/*
result:
Array
(
[0] =>
[1] => 1
[2] => 2
[3] =>
[4] => 3
[5] =>
)
*/
print_r(array_flip(array_flip($ar)));
/*
result:
Array
(
[1] => 1
[2] => 2
[4] => 3
)
*/
?>
Hayley Watson
20-Mar-2009 10:22
Finding the longest string in an array?
<?php
function longest_string_in_array($array)
{
$mapping = array_combine($array, array_map('strlen', $array));
return array_keys($mapping, max($mapping));
}
?>
Differences are obvious: returns an array of [i]all[/i] of the longest strings, instead of just picking one arbitrarily. Doesn't do the stripslashing or magic stuff because that's another job for for another function.
dan at aoindustries dot com
07-Mar-2009 08:48
From an algorithmic efficiency standpoint, building an entire array of lengths to then sort to only retrieve the longest value is unnecessary work. The following should be O(n) instead of O(n log n). It could also be:
<?php
function get_longest_value($array) {
// Some don't like to initialize, I do
$longest = NULL;
$longestLen = -1;
foreach ($array $value) {
$len = strlen($value);
if($len>$longestLen) {
$longest = $value;
$longestLen = $len;
}
}
$longest = str_replace("\r\n", "\n", $longest);
if (get_magic_quotes_gpc()) { return stripslashes($longest); }
return $longest;
}
?>
corz at corz dot org
08-Dec-2008 09:36
<?php
/*
Fun function to return the longest physical *value* from an array.
Culled from a small script designed to capture the longest $_POST variable,
usually the textarea, which would then be dumped to a "emergency post dump file".
corz at corz dot org
*/
$array = array("input" => "submit", "textarea" => "Some long spiel of text\r\na textarea, probably",
"another-input" => "make me longer", "and" => "another", "etc" => "etc.");
echo '<!DOCTYPE HTML SYSTEM><html><head><title>long</title></head><body><pre>Longest value: ',
get_longest_value($array),'</pre></body></html>';
function get_longest_value($array) {
foreach ($array as $key => $value) {
$lengths[$key] = strlen($value);
}
asort($lengths);
$lengths = array_flip($lengths);
$longest = str_replace("\r\n", "\n", $array[array_pop($lengths)]);
if (get_magic_quotes_gpc()) { return stripslashes($longest); }
return $longest;
}
?>
pinkgothic at gmail dot com
26-Apr-2007 08:37
In case anyone is wondering how array_flip() treats empty arrays:
<?php
print_r(array_flip(array()));
?>
results in:
Array
(
)
I wanted to know if it would return false and/or even chuck out an error if there were no key-value pairs to flip, despite being non-intuitive if that were the case. But (of course) everything works as expected. Just a head's up for the paranoid.
snaury at narod dot ru
23-Nov-2004 07:21
When you do array_flip, it takes the last key accurence for each value, but be aware that keys order in flipped array will be in the order, values were first seen in original array. For example, array:
[1] => 1
[2] => 2
[3] => 3
[4] => 3
[5] => 2
[6] => 1
[7] => 1
[8] => 3
[9] => 3
After flipping will become:
(first seen value -> first key)
[1] => 7
[2] => 5
[3] => 9
And not anything like this:
(last seen value -> last key)
[2] => 5
[1] => 7
[3] => 9
In my application I needed to find five most recently commented entries. I had a sorted comment-id => entry-id array, and what popped in my mind is just do array_flip($array), and I thought I now would have last five entries in the array as most recently commented entry => comment pairs. In fact it wasn't (see above, as it is the order of values used). To achieve what I need I came up with the following (in case someone will need to do something like that):
First, we need a way to flip an array, taking the first encountered key for each of values in array. You can do it with:
$array = array_flip(array_unique($array));
Well, and to achieve that "last comments" effect, just do:
$array = array_reverse($array, true);
$array = array_flip(array_unique($array));
$array = array_reverse($array, true);
In the example from the very beginning array will become:
[2] => 5
[1] => 7
[3] => 9
Just what I (and maybe you?) need. =^_^=
znailz at yahoo dot com
05-Aug-2003 09:42
I know a lot of people want a function to remove a key by value from an array. I saw solutions that iterate(!) though the whole array comparing value by value and then unsetting that value's key. PHP has a built-in function for pretty much everything (heard it will even cook you breakfast), so if you think "wouldn't it be cool if PHP had a function to do that...", odds are it already has. Check out this example. It takes a value, gets all keys for that value if it has duplicates, unsets them all, and returns a reindexed array.
<?php
$arr = array(11,12,13,12); // sample array
$arr = array_flip($arr);
unset($arr[12]);
$arr = array(array_keys($arr));
?>
$arr contains:
Array
(
[0] => Array
(
[0] => 11
[1] => 13
)
?>
)