array_filter
True, array_unique does preserve keys, but if you are incrementing in a loop, then it will stop once the key values break numerical order. If you don't care about preserving keys, a life-saver (originally a headache) for me was...
<?php
$new_array = array_keys(array_flip($old_array));
?>
i used this little snip-it after results from preg_match_all() as a way to remove duplicates from an array and then re-organize the numerical keys ;)
*Only works on arrays with numerical keys.
array_flip
(PHP 4, PHP 5)
array_flip — Scambia tutte le chiavi di un array con i loro valori associati
Descrizione
array array_flip
( array $trans
)
array_flip() restituisce un array scambiato, ovvero le chiavi di trans diventano valori e i valori di trans diventano chiavi.
Si noti che i valori di trans devono poter diventare chiavi valide, ovvero devo essere di tipo integer o string. Un errore verrà segnalato se un valore ha il tipo errato, e la coppia chiave/valore in questione non verrà scambiata.
Se un valore ha più di una occorrenza, L'ultima chiave verrà usata come valore, e tutte le altre verranno perse.
array_flip() restituisce FALSE se fallisce.
Example #1 Esempio di array_flip()
<?php
$trans = array_flip($trans);
$original = strtr($str, $trans);
?>
Example #2 Esempio di array_flip(): collisione
<?php
$trans = array("a" => 1, "b" => 1, "c" => 2);
$trans = array_flip($trans);
print_r($trans);
?>
ora $trans è:
Array ( [1] => b [2] => c )
Vedere anche array_values(), array_keys() e array_reverse().
add a note
User Contributed Notesarray_flip
Anonymous
29-Feb-2008 11:45
29-Feb-2008 11:45
eSeYaRr
28-Aug-2007 09:21
28-Aug-2007 09:21
In array_unique() user notes, you'll see that the flip flip use is faster than the array_unique() use for that purpose.
pinkgothic at gmail dot com
26-Apr-2007 01:37
26-Apr-2007 01:37
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.
http://www.callum-macdonald.com/
05-Mar-2007 10:13
05-Mar-2007 10:13
It might seem obvious, but if you want to remove duplicates from an array, you can use array_flip() twice:
$arr = array_flip(array_flip($arr));
mikeb at tracersinfo dot com
06-Feb-2006 02:42
06-Feb-2006 02:42
Further deriving on benles -> crescentfreshpot, I think the following restatement of array_invert() reads much easier and probably runs faster, too. It does yield the same results:
function array_invert($arr) {
$flipped = array();
foreach ( $arr as $k => $a ) {
# put the value in the key, with a throw-away value. dups are inherently avoided,
# though overwritten. not sure if prefixing with if ( !isset($flipped[$a][$k]) )
# would speed this up or slow it down. probably depends on quantity of dups.
$flipped[$a][$k] = NULL;
}
foreach ( $flipped as $k => $fl ) {
# now make the keys the values.
$flipped[$k] = array_keys($fl);
}
return $flipped;
}
crescentfreshpot at yahoo dot com
03-Jul-2005 04:21
03-Jul-2005 04:21
Furthering benles note, if you don't want duplicate values to overwrite existing keys but need non-duplicate values to be assigned like array_flip, use:
<?php
function array_invert($arr)
{
$flipped = array();
foreach(array_keys($arr) as $key) {
if(array_key_exists($arr[$key],$flipped)) {
$flipped[$arr[$key]] = array_merge((array)$flipped[$arr[$key]], (array)$key);
} else {
$flipped[$arr[$key]] = $key;
}
}
return $flipped;
}
$a = array(
'orange' => 'fruit',
'milk' => 'dairy',
'apple' => 'fruit',
'banana' => 'fruit'
);
print_r(array_invert($a));
/*
Output:
Array
(
[fruit] => Array
(
[0] => orange
[1] => apple
[2] => banana
)
[dairy] => milk
)
*/
?>
benles at bldigital dot com
05-Mar-2005 05:52
05-Mar-2005 05:52
In case anyone wants a function that doesn't lose duplicates:
function array_invert($arr)
{
$res = Array();
foreach(array_keys($arr) as $key)
{
if (!array_key_exists($arr[$key], $res)) $res[$arr[$key]] = Array();
array_push($res[$arr[$key]], $key);
}
return $res;
}
snaury at narod dot ru
23-Nov-2004 11:21
23-Nov-2004 11:21
When you do array_flip, it takes the last key accurence for each value, but be aware that keys order in flipped array will be in the order, values were first seen in original array. For example, array:
[1] => 1
[2] => 2
[3] => 3
[4] => 3
[5] => 2
[6] => 1
[7] => 1
[8] => 3
[9] => 3
After flipping will become:
(first seen value -> first key)
[1] => 7
[2] => 5
[3] => 9
And not anything like this:
(last seen value -> last key)
[2] => 5
[1] => 7
[3] => 9
In my application I needed to find five most recently commented entries. I had a sorted comment-id => entry-id array, and what popped in my mind is just do array_flip($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 02:42
05-Aug-2003 02:42
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:
<?php
Array
(
[0] => Array
(
[0] => 11
[1] => 13
)
?>
)
rgonzalez at kidchile dot cl
06-Mar-2003 11:58
06-Mar-2003 11:58
If you need traspose an array (i.e convert columns in rows) for a multidimensional array obtain from a SQL query, try this:
That is an array from arrays that represent each columns.
Array
(
[col1] => Array
(
[0] => 10
[1] => 100
[2] => 200
[3] => a
)
[col2] => Array
(
[0] => 1
[1] => 3
[2] => 2
[3] => 5
)
)
<?php
$arreglo_aux = Array();
foreach( $arreglo as $keymaster => $value )
foreach( $value as $key => $elemento )
$arreglo_aux[$key][$keymaster] = $elemento;
?>
the results will be
Array
(
[0] => Array
(
[col1] => 10
[col2] => 1
)
[1] => Array
(
[col1] => 100
[col2] => 3
)
[2] => Array
(
[col1] => 200
[col2] => 2
)
[3] => Array
(
[col1] => a
[col2] => 5
)
)
Bye.
Rodrigo González M. - CHILE