问题
is it possible to easily 'rotate' an array in PHP ?
Like this: 1, 2, 3, 4 -> 2, 3 ,4 ,1
Is there some kind of built-in PHP function for this?
回答1:
Most of the current answers are correct, but only if you don't care about your indices:
$arr = array('foo' => 'bar', 'baz' => 'qux', 'wibble' => 'wobble');
array_push($arr, array_shift($arr));
print_r($arr);
Output:
Array
(
[baz] => qux
[wibble] => wobble
[0] => bar
)
To preserve your indices you can do something like:
$arr = array('foo' => 'bar', 'baz' => 'qux', 'wibble' => 'wobble');
$keys = array_keys($arr);
$val = $arr[$keys[0]];
unset($arr[$keys[0]]);
$arr[$keys[0]] = $val;
print_r($arr);
Output:
Array
(
[baz] => qux
[wibble] => wobble
[foo] => bar
)
Perhaps someone can do the rotation more succinctly than my four-line method, but this works anyway.
回答2:
$numbers = array(1,2,3,4);
array_push($numbers, array_shift($numbers));
print_r($numbers);
Output
Array
(
[0] => 2
[1] => 3
[2] => 4
[3] => 1
)
回答3:
It's very simple and could be done in many ways. Example:
$array = array( 'a', 'b', 'c' );
$array[] = array_shift( $array );
回答4:
A method to maintain keys and rotate. using the same concept as array_push(array, array_shift(array)), instead we will use array_merge of 2 array_slices
$x = array("a" => 1, "b" => 2, "c" => 3, 'd' => 4);
To move the First element to the end
array_merge(array_slice($x, 1, NULL, true), array_slice($x, 0, 1, true)
//'b'=>2, 'c'=>3, 'd'=>4, 'a'=>1
To move the last element to the front
array_merge(array_slice($x, count($x) -1, 1, true), array_slice($x, 0,
//'d'=>4, 'a'=>1, 'b'=>2, 'c'=>3
回答5:
you can use this function:
function arr_rotate(&$array,$rotate_count) {
for ($i = 0; $i < $rotate_count; $i++) {
array_push($array, array_shift($array));
}
}
usage:
$xarr = array('1','2','3','4','5');
arr_rotate($xarr, 2);
print_r($xarr);
result:
Array ( [0] => 3 [1] => 4 [2] => 5 [3] => 1 [4] => 2 )
回答6:
Use array_shift and array_push.
回答7:
$daynamesArray = array("Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday");
array_push($daynamesArray, array_shift($daynamesArray)); //shift by one
array_push($daynamesArray, array_shift($daynamesArray)); //shift by two
print_r($daynamesArray);
The output starts at "Wednesday":
Array ( [0] => Wednesday [1] => Thursday [2] => Friday [3] => Saturday [4] => Sunday [5] => Monday [6] => Tuesday
回答8:
There's a task about array rotation on Hackerrank: https://www.hackerrank.com/challenges/array-left-rotation/problem.
And proposed solution with array_push and array_shift will work for all test cases except the last one, which fails due to timeout. So, array_push and array_shift will give you not the fastest solution.
Here's the faster approach:
function leftRotation(array $array, $n) {
for ($i = 0; $i < $n; $i++) {
$value = array[$i]; unset(array[$i]); array[] = $value;
}
return array;
}
回答9:
The logic is to swap the elements. Algorithm may look like -
for i = 0 to arrayLength - 1
swap( array[i], array[i+1] ) // Now array[i] has array[i+1] value and
// array[i+1] has array[i] value.
回答10:
No. Check the documentation for array_shift and its related functions for some tools you can use to write one. There might even be an array_rotate function implemented in the comments of that page.
It's also worth reading through the array functions listed on the left-hand sidebar to get a full understanding of what array functions are available in PHP.
回答11:
Looping through the array, and shift-ing and push-ing, may be a common way to rotate an array, however it can often mess up your keys. A more robust method is using a combination of array_merge and array_splice.
/**
* Rotates an array.
*
* Numerical indexes will be renumbered automatically.
* Associations will be kept for keys which are strings.
*
* Rotations will always occur similar to shift and push,
* where the number of items denoted by the distance are
* removed from the start of the array and are appended.
*
* Negative distances work in reverse, and are similar to
* pop and unshift instead.
*
* Distance magnitudes greater than the length of the array
* can be interpreted as rotating an array more than a full
* rotation. This will be reduced to calculate the remaining
* rotation after all full rotations.
*
* @param array $array The original array to rotate.
* Passing a reference may cause the original array to be truncated.
* @param int $distance The number of elements to move to the end.
* Distance is automatically interpreted as an integer.
* @return array The modified array.
*/
function array_rotate($array, $distance = 1) {
settype($array, 'array');
$distance %= count($array);
return array_merge(
array_splice($array, $distance), // Last elements - moved to the start
$array // First elements - appended to the end
);
}
// Example rotating an array 180°.
$rotated_180 = array_rotate($array, count($array) / 2);
Alternatively, if you also find the need to rotate keys so that they match with different values, you can combine array_keys, array_combine, array_rotate, and array_values.
/**
* Rotates the keys of an array while keeping values in the same order.
*
* @see array_rotate(); for function arguments and output.
*/
function array_rotate_key($array, $distance = 1) {
$keys = array_keys((array)$array);
return array_combine(
array_rotate($keys, $distance), // Rotated keys
array_values((array)$array) // Values
);
}
Or alternatively rotating the values while keeping the keys in the same order (equivalent to calling the negative distance on the matching array_rotate_key function call).
/**
* Rotates the values of an array while keeping keys in the same order.
*
* @see array_rotate(); for function arguments and output.
*/
function array_rotate_value($array, $distance = 1) {
$values = array_values((array)$array);
return array_combine(
array_keys((array)$array), // Keys
array_rotate($values, $distance) // Rotated values
);
}
And finally, if you want to prevent renumbering of numerical indexes.
/**
* Rotates an array while keeping all key and value association.
*
* @see array_rotate(); for function arguments and output.
*/
function array_rotate_assoc($array, $distance = 1) {
$keys = array_keys((array)$array);
$values = array_values((array)$array);
return array_combine(
array_rotate($keys, $distance), // Rotated keys
array_rotate($values, $distance) // Rotated values
);
}
It could be beneficial to perform some benchmark tests, however, I expect that a small handful of rotations per request wouldn't affect performance noticeably regardless of which method is used.
It should also be possible to rotate an array by using a custom sorting function, but it would most likely be overly complicated. i.e. usort.
回答12:
Yes it is, here is a function I did myself, where $A is the array and $K the number of times you want to rotate the array:
function solution($A, $K) {
for($i = 0; $i < $K; $i++): //we cycle $K
$arrayTemp = $A;
for($j = 0; $j < count($arrayTemp); $j++): // we cycle the array
if($j == count($arrayTemp) - 1) $A[0] = $arrayTemp[$j]; // we check for the last position
else $A[$j + 1] = $arrayTemp[$j]; // all but last position
endfor;
endfor;
return $A;
}
回答13:
Please use the build in function array_reverse. It is the fastest way to 'rotate' a array in php.
http://php.net/manual/de/function.array-reverse.php
来源：https://stackoverflow.com/questions/5601707/php-rotate-an-array