例如,我有一个包含 4 个元素的数组array("a", "b", "c", d");
,重复此数组以创建具有一定长度的新数组(例如 71 个元素)的最快方法是什么?
10 回答
// the variables
$array = array("a", "b", "c", "d");
$desiredLength = 71;
$newArray = array();
// create a new array with AT LEAST the desired number of elements by joining the array at the end of the new array
while(count($newArray) <= $desiredLength){
$newArray = array_merge($newArray, $array);
}
// reduce the new array to the desired length (as there might be too many elements in the new array
$array = array_slice($newArray, 0, $desiredLength);
使用 SPL InfiniteIterator的解决方案:
<?php
function fillArray1($length, $values) {
foreach (new InfiniteIterator(new ArrayIterator($values)) as $element) {
if (!$length--) return $result;
$result[] = $element;
}
return $result;
}
var_dump(fillArray(71, array('a', 'b', 'c', 'd')));
真正的 SPL 黑客可能已经放弃了if (!$length--) break;
,而是使用了限制迭代器:new LimitIterator(new InfiniteIterator(new ArrayIterator($values)), 0, $length)
,但我认为这太过分了......
使用each()
andreset()
和数组的内部指针的简单解决方案:
<?php
$array = array('a', 'b', 'c', 'd');
$length = 71;
$result = array();
while(count($result) < $length)
{
$current = each($array);
if($current == false)
{
reset($array);
continue;
}
$result[] = $current[1];
}
echo count($result); // Output: 71
为了加入这个俱乐部:
$result = call_user_func_array('array_merge', array_fill(0, ceil($size/count($array)), $array));
while(count($result) > $size) array_pop($result);
你要求最快,所以我做了一个基准测试(来源: http: //pastebin.com/G5w7QJPU)
Kau-Boy: 5.40128803253
Frxstrem: 5.00970411301
NikiC: 4.12150001526
user2469998: 0.561513900757
Alexander: 1.92847204208
Hammerite: 2.17130494118
Max: 12.9516701698
Evert: 1.9378361702
Christoph: 1.6862449646
Test took 35.7696909904s
user2469998 是最快的,但它仅适用于具有单个字符的字符串值(或者如果使用 str_split 的第二个参数,则长度相同)。
$array = array("a", "b", "c", "d");
$merge = array();
$desiredLength = 71;
while(2 * count($array) <= $desiredLength){
$array = array_merge($array, $array);
}
if($desiredLength > count($array))
$merge = array_slice($array, 0, $desiredLength - count($array));
$array = array_merge($array, $merge);
$array = array_slice($array, 0, $desiredLength);
print_r($array);
$newarray = array();
$i = 0;
$oldarrayvalues = array_values($oldarray);
$oldarraysize = count($oldarrayvalues);
if ( $oldarraysize ) {
while ( count($newarray) < DESIRED_ARRAY_SIZE ) {
$newarray[] = $oldarrayvalues[$i];
$i++;
$i %= $oldarraysize;
}
}
<?php
$array = array('a', 'b', 'c', 'd');
$end = 71;
$new_array = array();
while(count($new_array) <= $end)
{
foreach($array as $key => $value)
{
$new_array[] = $value;
}
}
$new_array = array_slice($new_array, 0, $end);
Tested and works.
You can test for yourself by adding this:
echo '<pre>';
print_r($new_array);
echo '</pre>';
$arr = array("a", "b", "c", "d");
$len = 71;
$a = array();
$a = str_split( substr( str_repeat( join( $arr), ceil( $len / count( $arr))), 0, $len));
var_export($a);
如果你有 PHP 5.3 可用,你也可以试试这个:
function fill(array $initalArray, $toCount) {
$initialArrayCount = count($initalArray);
$fillUp = function(array $filledUpArray, $missingCount)
use(&$fillUp, $initalArray, $initialArrayCount, $toCount)
{
if($missingCount <= 0) return array_slice($filledUpArray, 0, $toCount);
return $fillUp(array_merge($filledUpArray, $initalArray), $missingCount - $initialArrayCount);
};
return $fillUp($initalArray, $toCount - $initialArrayCount);
}
$theArray = array("a", "b", "c", "d");
$toLength = 71;
$filledArray = fill($theArray, $toLength);
print_r($filledArray);
我认为 user2469998 是最接近的,但不是那么好。
在我的示例中,我使用管道内爆和 str_repeat 函数来构建符合长度的字符串,将其炸开并修剪脂肪。
$list = array('a','b','c','d');
$length = 6;
$result = array_slice(explode('|', str_repeat(implode('|', $list).'|',ceil($length/count($list)))), 0, $length);
实现这一目标的方法很多,但我想我会分享我的。唯一的限制是您需要使用不属于数组项的角色来内爆和爆炸,否则爆炸器将无法正常工作。
:)