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));
array_flip
(PHP 4, PHP 5)
array_flip — 配列のキーと値を反転する
説明
array array_flip ( array trans )array_flip() は、配列を反転して返します。 すなわち、trans のキーが値となり、 trans の値がキーとなります。
trans の値は有効なキーを必要とすることに注意してください。 すなわち、キーは、integer または string である必要があります。ある値が間違った型である場合、 警告が出力され、問題のこのキー/値の組は逆順にされません。
ある値が複数回出現した場合、最後のキーがその値として使用され、 その他の値は失われます。
array_flip() は、失敗した場合に FALSE を返します。
例 227. array_flip() の例 : 衝突
<?php
$trans = array("a" => 1, "b" => 1, "c" => 2);
$trans = array_flip($trans);
print_r($trans);
?>
$trans は次のようになります:
Array
(
[1] => b
[2] => c
)
array_values()、 array_keys() および array_reverse() も参照ください。
array_flip
http://www.callum-macdonald.com/
06-Mar-2007 03:13
06-Mar-2007 03:13
mikeb at tracersinfo dot com
07-Feb-2006 07:42
07-Feb-2006 07:42
Further deriving on benles -> crescentfreshpot, I think the following restatement of array_invert() reads much easier and probably runs faster, too. It does yield the same results:
function array_invert($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 $flipped;
}
crescentfreshpot at yahoo dot com
04-Jul-2005 08:21
04-Jul-2005 08:21
Furthering benles note, if you don't want duplicate values to overwrite existing keys but need non-duplicate values to be assigned like array_flip, use:
<?php
function array_invert($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 10:52
06-Mar-2005 10:52
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 $res;
}
snaury at narod dot ru
24-Nov-2004 04:21
24-Nov-2004 04:21
When you do array_flip, it takes the last key accurence for each value, but be aware that keys order in flipped array will be in the order, values were first seen in original array. For example, array:
[1] => 1
[2] => 2
[3] => 3
[4] => 3
[5] => 2
[6] => 1
[7] => 1
[8] => 3
[9] => 3
After flipping will become:
(first seen value -> first key)
[1] => 7
[2] => 5
[3] => 9
And not anything like this:
(last seen value -> last key)
[2] => 5
[1] => 7
[3] => 9
In my application I needed to find five most recently commented entries. I had a sorted comment-id => entry-id array, and what popped in my mind is just do array_flip($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 06:42
06-Aug-2003 06:42
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
07-Mar-2003 04:58
07-Mar-2003 04:58
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 Gonzlez M. - CHILE