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Last updated: Sat, 27 Jan 2007

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# array_flip

(PHP 4, PHP 5)

array_flip -- Поменять местами значения массива

## Описание

array array_flip ( array input )

Функция array_flip() возвращает array в обратном порядке, то есть ключи массива `input` становятся значениями, а значения массива `input` становятся ключами.

Обратите внимание, что значения массива `input` должны быть корректными ключами, то есть они должны иметь тип integer или string. Если значение имеет неверный тип, будет выдано предупреждение и пара ключ/значение не будет обработана.

Если значение встречается несколько раз, для обработки будет использоваться последний встреченный ключ, а все остальные будут потеряны.

Функция array_flip() возвращает `FALSE`, если обработка массива вызвала ошибку.

Пример 1. Пример использования array_flip()

`$trans = array_flip ($trans); $original = strtr ($str, $trans);`

Пример 2. Пример использования array_flip(): многократное повторение значения

`$trans = array ("a" => 1, "b" => 1, "c" => 2); $trans = array_flip ($trans); print_r($trans);`

теперь $trans содержит:

    Array
    (
        [1] => b
        [2] => c
    )

add a note User Contributed Notes
array_flip
http://www.callum-macdonald.com/
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
`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 $flipped;
}`
crescentfreshpot at yahoo dot com
03-Jul-2005 04:21
`Furthering benles note, if you don't want duplicate values to overwrite existing keys but need non-duplicate values to be assigned like array_flip, use:
<?php
function array_invert($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
`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 $res;
}`
snaury at narod dot ru
23-Nov-2004 11:21
`When you do array_flip, it takes the last key accurence for each value, but be aware that keys order in flipped array will be in the order, values were first seen in original array. For example, array:
[1] => 1
[2] => 2
[3] => 3
[4] => 3
[5] => 2
[6] => 1
[7] => 1
[8] => 3
[9] => 3
After flipping will become:
(first seen value -> first key)
[1] => 7
[2] => 5
[3] => 9
And not anything like this:
(last seen value -> last key)
[2] => 5
[1] => 7
[3] => 9
In my application I needed to find five most recently commented entries. I had a sorted comment-id => entry-id array, and what popped in my mind is just do array_flip($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
`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
`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 Gonz�lez M. - CHILE`
add a note
array_intersect_assoc array_filter

Last updated: Sat, 27 Jan 2007
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