array_filter
using array_flip(array_flip($array)) or array_keys(array_flip($array)) as key-collapsing alternatives to array_unique() makes your intention less apparent. Try:
array_values(array_unique($array))
as a more readable alternative.
array_flip
(PHP 4, PHP 5)
array_flip — 交换数组中的键和值
说明
array array_flip
( array $trans
)
array_flip() 返回一个反转后的 array，例如 trans 中的键名变成了值，而 trans 中的值成了键名。
注意 trans 中的值需要能够作为合法的键名，例如需要是 integer 或者 string。如果值的类型不对将发出一个警告，并且有问题的键／值对将不会反转。
如果同一个值出现了多次，则最后一个键名将作为它的值，所有其它的都丢失了。
array_flip() 如果失败返回 FALSE。
Example#1 array_flip() 例子
<?php
$trans = array_flip($trans);
$original = strtr($str, $trans);
?>
Example#2 array_flip() 例子：冲突
<?php
$trans = array("a" => 1, "b" => 1, "c" => 2);
$trans = array_flip($trans);
print_r($trans);
?>
现在 $trans 变成了：
Array ( [1] => b [2] => c )
add a note
User Contributed Notesarray_flip
rdanner
21-Aug-2008 09:17
21-Aug-2008 09:17
Anonymous
01-Mar-2008 03:45
01-Mar-2008 03:45
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.
eSeYaRr
29-Aug-2007 12:21
29-Aug-2007 12:21
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 04:37
26-Apr-2007 04:37
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/
06-Mar-2007 02:13
06-Mar-2007 02:13
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
07-Feb-2006 06:42
07-Feb-2006 06:42
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 $flipped;
}
crescentfreshpot at yahoo dot com
04-Jul-2005 07:21
04-Jul-2005 07:21
Furthering benles note, if you don't want duplicate values to overwrite existing keys but need non-duplicate values to be assigned like array_flip, use:
<?php
function array_invert($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
06-Mar-2005 09:52
06-Mar-2005 09:52
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 $res;
}
snaury at narod dot ru
24-Nov-2004 03:21
24-Nov-2004 03:21
When you do array_flip, it takes the last key accurence for each value, but be aware that keys order in flipped array will be in the order, values were first seen in original array. For example, array:
[1] => 1
[2] => 2
[3] => 3
[4] => 3
[5] => 2
[6] => 1
[7] => 1
[8] => 3
[9] => 3
After flipping will become:
(first seen value -> first key)
[1] => 7
[2] => 5
[3] => 9
And not anything like this:
(last seen value -> last key)
[2] => 5
[1] => 7
[3] => 9
In my application I needed to find five most recently commented entries. I had a sorted comment-id => entry-id array, and what popped in my mind is just do array_flip($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
06-Aug-2003 05:42
06-Aug-2003 05:42
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
)
?>
)