array_flip
Функция array_flip() возвращает array наоборот, то есть ключи массива array становятся значениями, а значения массива array становятся ключами.
Обратите внимание, что значения массива array должны быть корректными ключами, то есть они должны иметь тип integer или string . Если значение имеет неверный тип, будет выдано предупреждение и данная пара ключ/значение не будет включена в результат.
Если значение встречается несколько раз, для обработки будет использоваться последний встреченный ключ, а все остальные будут потеряны.
Список параметров
Массив переворачиваемых пар ключ/значение.
Возвращаемые значения
Возвращает перевернутый массив в случае успеха, или NULL в случае ошибки.
Примеры
Пример #1 Пример использования array_flip()
$input = array( «oranges» , «apples» , «pears» );
$flipped = array_flip ( $input );
Результат выполнения данного примера:
Array ( [oranges] => 0 [apples] => 1 [pears] => 2 )
Пример #2 Пример использования array_flip() с коллизиями
$input = array( «a» => 1 , «b» => 1 , «c» => 2 );
$flipped = array_flip ( $input );
Результат выполнения данного примера:
Смотрите также
- array_values() — Выбирает все значения массива
- array_keys() — Возвращает все или некоторое подмножество ключей массива
- array_reverse() — Возвращает массив с элементами в обратном порядке
array_flip
array_flip() returns an array in flip order, i.e. keys from array become values and values from array become keys.
Note that the values of array need to be valid keys, i.e. they need to be either int or string . A warning will be emitted if a value has the wrong type, and the key/value pair in question will not be included in the result.
If a value has several occurrences, the latest key will be used as its value, and all others will be lost.
Parameters
An array of key/value pairs to be flipped.
Return Values
Returns the flipped array.
Examples
Example #1 array_flip() example
$input = array( «oranges» , «apples» , «pears» );
$flipped = array_flip ( $input );
The above example will output:
Array ( [oranges] => 0 [apples] => 1 [pears] => 2 )
Example #2 array_flip() example : collision
$input = array( «a» => 1 , «b» => 1 , «c» => 2 );
$flipped = array_flip ( $input );
The above example will output:
See Also
- array_values() — Return all the values of an array
- array_keys() — Return all the keys or a subset of the keys of an array
- array_reverse() — Return an array with elements in reverse order
User Contributed Notes 19 notes
I find this function vey useful when you have a big array and you want to know if a given value is in the array. in_array in fact becomes quite slow in such a case, but you can flip the big array and then use isset to obtain the same result in a much faster way.
This function is useful when parsing a CSV file with a heading column, but the columns might vary in order or presence:
/* Take the first line (the header) into an array, then flip it
so that the keys are the column name, and values are the
column index. */
$cols = array_flip ( fgetcsv ( $f ));
while ( $line = fgetcsv ( $f ))
// Now we can reference CSV columns like so:
$status = $line [ $cols [ ‘OrderStatus’ ]];
>
?>
I find this better than referencing the numerical array index.
array_flip will remove duplicate values in the original array when you flip either an associative or numeric array. As you might expect it’s the earlier of two duplicates that is lost:
$a = array( ‘one’ , ‘two’ , ‘one’ );
print_r ( $a );
$b = array_flip ( $a );
print_r ( $b );
?>
Result:
array(3) [0] => string(3) «one»
[1] => string(3) «two»
[2] => string(3) «one»
>
This may be good or bad, depending on what you want, but no error is thrown.
array_flip() does not retain the data type of values, when converting them into keys. 🙁
$arr = array( ‘one’ => ‘1’ , ‘two’ => ‘2’ , ‘three’ => ‘3’ );
var_dump ( $arr );
$arr2 = array_flip ( $arr );
var_dump ( $arr2 );
?>
This code outputs this:
array(3) [«one»]=>
string(1) «1»
[«two»]=>
string(1) «2»
[«three»]=>
string(1) «3»
>
array(3) [1]=>
string(3) «one»
[2]=>
string(3) «two»
[3]=>
string(5) «three»
>
It is valid expectation that string values «1», «2» and «3» would become string keys «1», «2» and «3».
When you do array_flip, it takes the last key accurence for each value, but be aware that keys order in flipped array will be in the order, values were first seen in original array. For example, array:
After flipping will become:
(first seen value -> first key)
And not anything like this:
(last seen value -> last key)
In my application I needed to find five most recently commented entries. I had a sorted comment-id => entry-id array, and what popped in my mind is just do array_flip($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:
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:
Just what I (and maybe you?) need. =^_^=
In case anyone is wondering how array_flip() treats empty arrays:
print_r ( array_flip (array()));
?>
results in:
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.
I needed a way to flip a multidimensional array and came up with this function to accomplish the task. I hope it helps someone else.
function multi_array_flip ( $arrayIn , $DesiredKey , $DesiredKey2 = false , $OrigKeyName = false ) <
$ArrayOut =array();
foreach ( $arrayIn as $Key => $Value )
<
// If there is an original key that need to be preserved as data in the new array then do that if requested ($OrigKeyName=true)
if ( $OrigKeyName ) $Value [ $OrigKeyName ]= $Key ;
// Require a string value in the data part of the array that is keyed to $DesiredKey
if (! is_string ( $Value [ $DesiredKey ])) return false ;
// If $DesiredKey2 was specified then assume a multidimensional array is desired and build it
if ( is_string ( $DesiredKey2 ))
<
// Require a string value in the data part of the array that is keyed to $DesiredKey2
if (! is_string ( $Value [ $DesiredKey2 ])) return false ;
// Build NEW multidimensional array
$ArrayOut [ $Value [ $DesiredKey ]][ $Value [ $DesiredKey2 ]]= $Value ;
>
// Build NEW single dimention array
else $ArrayOut [ $Value [ $DesiredKey ]][]= $Value ;
>
return $ArrayOut ;
> //end multi_array_flip
?>
If you don’t want to lose duplicates, and you’re ok, with having the values in the flipped array in an array as well, you may use this:
function array_flip_safe (array $array ) : array
return array_reduce ( array_keys ( $array ), function ( $carry , $key ) use (& $array ) $carry [ $array [ $key ]] ??= [];
$carry [ $array [ $key ]][] = $key ;
return $carry ;
>, []);
>
?>
PHP 7.0 — ^7.3 (Time to upgrade to PHP 8 ^^)
function array_flip_safe (array $array ) : array
return array_reduce ( array_keys ( $array ), function ( $carry , $key ) use (& $array ) $carry [ $array [ $key ]] = $carry [ $array [ $key ]] ?? [];
$carry [ $array [ $key ]][] = $key ;
return $carry ;
>, []);
>
function array_flip_safe (array $array )
return array_reduce ( array_keys ( $array ), function ( $carry , $key ) use (& $array ) if (!isset( $carry [ $array [ $key ]])
$carry [ $array [ $key ]] = [];
$carry [ $array [ $key ]][] = $key ;
return $carry ;
>, []);
>
Don’t use this function for filtering or searching an array — PHP already has functions for exactly those purposes. If nothing else, array_flip will trash the array’s elements if they’re anything other than integers or non-decimal-integer strings.
$arr = array( ‘one’ => [ ‘four’ => 4 ], ‘two’ => ‘2’ , ‘three’ => ‘3’ );
var_dump ( $arr );
$arr2 = array_flip ( $arr );
var_dump ( $arr2 );
?>
The above example will output:
Warning: array_flip(): Can only flip STRING and INTEGER values! in /root/test.php on line 4
array(2) [2]=>
string(3) «two»
[3]=>
string(5) «three»
>
Similarly, if you want the last value without affecting the pointer, you can do:
$array = array( «one» , «two» , «three» );
$last = array_pop ( array_keys ( array_flip ( $array )));
echo current ( $array ); // «two»
Finding the longest string in an array?
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.
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:
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 ;
>
?>
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.
$arr = array( 11 , 12 , 13 , 12 ); // sample array
$arr = array_flip ( $arr );
unset( $arr [ 12 ]);
$arr = array( array_keys ( $arr ));
?>
$arr contains:
Как поменять местами элементы php массива
Также поменять два элемента местами можно следующим способом:
$a = [1, 2]; [$a[1], $a[0]] = $a; print_r($a); // [ // [0] => 2 // [1] => 1 // ] Очень просто! Для этого нужно использовать промежуточную переменную, в которую мы сохраним один из элементов. Ниже пример того как это делается:
$items = [1, 'two', false]; // Поменяем местами первый и последний элемент // Сохраняем первый элемент в переменную $temp $temp = $items[0]; // Заменяем первый элемент массива последним $items[0] = $items[2]; // А теперь заменяем последний элемент значением из переменной $temp $items[2] = $temp; // Итоговый массив // [ // false, // "two", // 1, // ]