Ok,
我知道所有关于array_pop()，但它删除了最后一个元素。如何获得数组的最后一个元素而不删除它?
这里有一个奖励:
$array = array('a' => 'a', 'b' => 'b', 'c' => 'c');
甚至
$array = array('a', 'b', 'c', 'd');
unset($array[2]);
echo $array[sizeof($array) - 1]; // Output: PHP Notice: Undefined offset: 2 in - on line 4
当前回答
如何:
current(array_slice($array, -1))
适用于关联数组 当$array ==[](返回false)时生效 不会影响原始数组
其他回答
现在，我更喜欢一直有这个帮手，就像在php.net/end上建议的那样。
<?php
function endc($array) {
return end($array);
}
$items = array('one','two','three');
$lastItem = endc($items); // three
$current = current($items); // one
?>
这将始终保持指针的原样，我们将永远不必担心括号，严格的标准或其他。
要获取数组的最后一个元素，使用:
$lastElement = array_slice($array, -1)[0];
基准
我迭代了1,000次，分别获取包含100个和50,000个元素的小型和大型数组的最后一个元素。
Method: $array[count($array)-1];
Small array (s): 0.000319957733154
Large array (s): 0.000526905059814
Note: Fastest! count() must access an internal length property.
Note: This method only works if the array is naturally-keyed (0, 1, 2, ...).
Method: array_slice($array, -1)[0];
Small array (s): 0.00145292282104
Large array (s): 0.499367952347
Method: array_pop((array_slice($array, -1, 1)));
Small array (s): 0.00162816047668
Large array (s): 0.513121843338
Method: end($array);
Small array (s): 0.0028350353241
Large array (s): 4.81077480316
Note: Slowest...
我使用的是PHP 5.5.32版本。
这篇文章中的许多答案为我们提供了许多不同的选择。为了能够从中做出选择，我需要了解他们的行为和表现。在这个答案中，我将与您分享我的发现，以PHP版本5.6.38,7.2.10和7.3.0RC1为基准(预计2018年12月13日)。
我将测试的选项(<<选项代码>>s)是:
option .1. $x = array_values(array_slice($array, -1))[0]; (as suggested by rolacja) option .2. $x = array_slice($array, -1)[0]; (as suggested by Stoutie) option .3. $x = array_pop((array_slice($array, -1))); (as suggested by rolacja) option .4. $x = array_pop((array_slice($array, -1, 1))); (as suggested by Westy92) option .5. $x = end($array); reset($array); (as suggested by Iznogood) option .6. $x = end((array_values($array))); (as suggested by TecBrat) option .7. $x = $array[count($array)-1]; (as suggested by Mirko Pagliai) option .8. $keys = array_keys($array); $x = $array[$keys[count($keys)-1]]; (as suggested by thrau) option .9. $x = $array[] = array_pop($array); (as suggested by user2782001) option 10. $x = $array[array_key_last($array)]; (as suggested by Quasimodo's clone ; available per PHP 7.3)
(函数提到:array_key_last, array_keys, array_pop, array_slice, array_values, count, end, reset)
将测试输入(<<输入代码>>s)与:
Null = $array = Null; Empty = $array = []; Last_null = $array = ["a"，"b"，"c"，null]; Auto_idx = $array = ["a"，"b"，"c"，"d"]; Shuffle = $array = [];$array[1] = "a";$array[2] = "b";$array[0] = "c"; 100 = $array = [];For ($i=0;$i<100;$i++) {$array[] = $i;｝ 100000 = $array = [];$i=0;$i<100000;$i++) {$array[] = $i;｝
为了测试，我将使用5.6.38、7.2.10和7.3.0RC1 PHP docker容器，例如:
sudo docker run -it --rm php:5.6.38-cli-stretch php -r '<<<CODE HERE>>>'
上面列出的<<选项代码>>s和<<输入代码>>s的每个组合将在所有版本的PHP上运行。对于每个测试运行，使用以下代码片段:
<<input code>> error_reporting(E_ALL); <<option code>> error_reporting(0); $before=microtime(TRUE); for($i=0;$i<100;$i++){echo ".";for($j=0;$j<100;$j++){ <<option code>> }}; $after=microtime(TRUE); echo "\n"; var_dump($x); echo round(($after-$before)/(100*100)*1000*1000*1000);
对于每次运行，这将var_dump最后检索到的测试输入的最后一个值，并以飞秒为单位打印一次迭代的平均持续时间(0.000000000000001分之一秒)。
结果如下:
/==========================================================================================================================================================================================================================================================================================================================================================================================================================\
|| || T E S T I N P U T - 5 . 6 . 3 8 || T E S T I N P U T - 7 . 2 . 1 0 || T E S T I N P U T - 7 . 3 . 0 R C 1 ||
|| || null | empty | last_null | auto_idx | shuffle | 100 | 100000 || null | empty | last_null | auto_idx | shuffle | 100 | 100000 || null | empty | last_null | auto_idx | shuffle | 100 | 100000 ||
||============================OPTIONS - ERRORS==========================++===============+===============+===============+===============+===============+===============+===============++===============+===============+===============+===============+===============+===============+===============++===============+===============+===============+===============+===============+===============+===============<|
|| 1. $x = array_values(array_slice($array, -1))[0]; || W1 + W2 | N1 | - | - | - | - | - || W1 + W2 | N1 | - | - | - | - | - || W1 + W2 | N1 | - | - | - | - | - ||
|| 2. $x = array_slice($array, -1)[0]; || W1 | N1 | - | - | - | - | - || W1 | N1 | - | - | - | - | - || W1 | N1 | - | - | - | - | - ||
|| 3. $x = array_pop((array_slice($array, -1))); || W1 + W3 | - | - | - | - | - | - || W1 + N2 + W3 | N2 | N2 | N2 | N2 | N2 | N2 || W1 + N2 + W3 | N2 | N2 | N2 | N2 | N2 | N2 ||
|| 4. $x = array_pop((array_slice($array, -1, 1))); || W1 + W3 | - | - | - | - | - | - || W1 + N2 + W3 | N2 | N2 | N2 | N2 | N2 | N2 || W1 + N2 + W3 | N2 | N2 | N2 | N2 | N2 | N2 ||
|| 5. $x = end($array); reset($array); || W4 + W5 | - | - | - | - | - | - || W4 + W5 | N2 | N2 | N2 | N2 | N2 | N2 || W4 + W5 | - | - | - | - | - | - ||
|| 6. $x = end((array_values($array))); || W2 + W4 | - | - | - | - | - | - || W2 + N2 + W4 | - | - | - | - | - | - || W2 + N2 + W4 | N2 | N2 | N2 | N2 | N2 | N2 ||
|| 7. $x = $array[count($array)-1]; || - | N3 | - | - | - | - | - || W7 | N3 | - | - | - | - | - || W7 | N3 | - | - | - | - | - ||
|| 8. $keys = array_keys($array); $x = $array[$keys[count($keys)-1]]; || W6 | N3 + N4 | - | - | - | - | - || W6 + W7 | N3 + N4 | - | - | - | - | - || W6 + W7 | N3 + N4 | - | - | - | - | - ||
|| 9. $x = $array[] = array_pop($array); || W3 | - | - | - | - | - | - || W3 | - | - | - | - | - | - || W3 | - | - | - | - | - | - ||
|| 10. $x = $array[array_key_last($array)]; || F1 | F1 | F1 | F1 | F1 | F1 | F1 || F2 | F2 | F2 | F2 | F2 | F2 | F2 || W8 | N4 | F2 | F2 | F2 | F2 | F2 ||
||========================OPTIONS - VALUE RETRIEVED=====================++===============+===============+===============+===============+===============+===============+===============++===============+===============+===============+===============+===============+===============+===============++===============+===============+===============+===============+===============+===============+===============<|
|| 1. $x = array_values(array_slice($array, -1))[0]; || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) ||
|| 2. $x = array_slice($array, -1)[0]; || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) ||
|| 3. $x = array_pop((array_slice($array, -1))); || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) ||
|| 4. $x = array_pop((array_slice($array, -1, 1))); || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) ||
|| 5. $x = end($array); reset($array); || NULL | bool(false) | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | bool(false) | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | bool(false) | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) ||
|| 6. $x = end((array_values($array))); || NULL | bool(false) | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | bool(false) | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | bool(false) | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) ||
|| 7. $x = $array[count($array)-1]; || NULL | NULL | NULL | string(1) "d" | string(1) "b" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "b" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "b" | int(99) | int(99999) ||
|| 8. $keys = array_keys($array); $x = $array[$keys[count($keys)-1]]; || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) ||
|| 9. $x = $array[] = array_pop($array); || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) || NULL | NULL | NULL | string(1) "d" | string(1) "c" | int(99) | int(99999) ||
|| 10. $x = $array[array_key_last($array)]; || N/A | N/A | N/A | N/A | N/A | N/A | N/A || N/A | N/A | N/A | N/A | N/A | N/A | N/A || N/A | N/A | N/A | N/A | N/A | N/A | N/A ||
||=================OPTIONS - FEMTOSECONDS PER ITERATION=================++===============+===============+===============+===============+===============+===============+===============++===============+===============+===============+===============+===============+===============+===============++===============+===============+===============+===============+===============+===============+===============<|
|| 1. $x = array_values(array_slice($array, -1))[0]; || 803 | 466 | 390 | 384 | 373 | 764 | 1.046.642 || 691 | 252 | 101 | 128 | 93 | 170 | 89.028 || 695 | 235 | 90 | 97 | 95 | 188 | 87.991 ||
|| 2. $x = array_slice($array, -1)[0]; || 414 | 349 | 252 | 248 | 246 | 604 | 1.038.074 || 373 | 249 | 85 | 91 | 90 | 164 | 90.750 || 367 | 224 | 78 | 85 | 80 | 155 | 86.141 ||
|| 3. $x = array_pop((array_slice($array, -1))); || 724 | 228 | 323 | 318 | 350 | 673 | 1.042.263 || 988 | 285 | 309 | 317 | 331 | 401 | 88.363 || 877 | 266 | 298 | 300 | 326 | 403 | 87.279 ||
|| 4. $x = array_pop((array_slice($array, -1, 1))); || 734 | 266 | 358 | 356 | 349 | 699 | 1.050.101 || 887 | 288 | 316 | 322 | 314 | 408 | 88.402 || 935 | 268 | 335 | 315 | 313 | 403 | 86.445 ||
|| 5. $x = end($array); reset($array); || 715 | 186 | 185 | 180 | 176 | 185 | 172 || 674 | 73 | 69 | 70 | 66 | 65 | 70 || 693 | 65 | 85 | 74 | 68 | 70 | 69 ||
|| 6. $x = end((array_values($array))); || 877 | 205 | 320 | 337 | 304 | 2.901 | 7.921.860 || 948 | 300 | 336 | 308 | 309 | 509 | 29.696.951 || 946 | 262 | 301 | 309 | 302 | 499 | 29.234.928 ||
|| 7. $x = $array[count($array)-1]; || 123 | 300 | 137 | 139 | 143 | 140 | 144 || 312 | 218 | 48 | 53 | 45 | 47 | 51 || 296 | 217 | 46 | 44 | 53 | 53 | 55 ||
|| 8. $keys = array_keys($array); $x = $array[$keys[count($keys)-1]]; || 494 | 593 | 418 | 435 | 399 | 3.873 | 12.199.450 || 665 | 407 | 103 | 109 | 114 | 431 | 30.053.730 || 647 | 445 | 91 | 95 | 96 | 419 | 30.718.586 ||
|| 9. $x = $array[] = array_pop($array); || 186 | 178 | 175 | 188 | 180 | 181 | 186 || 83 | 78 | 75 | 71 | 74 | 69 | 83 || 71 | 64 | 70 | 64 | 68 | 69 | 81 ||
|| 10. $x = $array[array_key_last($array)]; || N/A | N/A | N/A | N/A | N/A | N/A | N/A || N/A | N/A | N/A | N/A | N/A | N/A | N/A || 370 | 223 | 49 | 52 | 61 | 57 | 52 ||
\=========================================================================================================================================================================================================================================================================================================================================================================================================================/
上述“致命”、“警告”和“通知”代码翻译为:
F1 = Fatal error: Call to undefined function array_key_last() in Command line code on line 1
F2 = Fatal error: Uncaught Error: Call to undefined function array_key_last() in Command line code:1
W1 = Warning: array_slice() expects parameter 1 to be array, null given in Command line code on line 1
W2 = Warning: array_values() expects parameter 1 to be array, null given in Command line code on line 1
W3 = Warning: array_pop() expects parameter 1 to be array, null given in Command line code on line 1
W4 = Warning: end() expects parameter 1 to be array, null given in Command line code on line 1
W5 = Warning: reset() expects parameter 1 to be array, null given in Command line code on line 1
W6 = Warning: array_keys() expects parameter 1 to be array, null given in Command line code on line 1
W7 = Warning: count(): Parameter must be an array or an object that implements Countable in Command line code on line 1
W8 = Warning: array_key_last() expects parameter 1 to be array, null given in Command line code on line 1
N1 = Notice: Undefined offset: 0 in Command line code on line 1
N2 = Notice: Only variables should be passed by reference in Command line code on line 1
N3 = Notice: Undefined offset: -1 in Command line code on line 1
N4 = Notice: Undefined index: in Command line code on line 1
基于这一输出，我得出以下结论:
newer versions of PHP perform better with the exception of these options that became significantly slower: option .6. $x = end((array_values($array))); option .8. $keys = array_keys($array); $x = $array[$keys[count($keys)-1]]; these options scale best for very large arrays: option .5. $x = end($array); reset($array); option .7. $x = $array[count($array)-1]; option .9. $x = $array[] = array_pop($array); option 10. $x = $array[array_key_last($array)]; (since PHP 7.3) these options should only be used for auto-indexed arrays: option .7. $x = $array[count($array)-1]; (due to use of count) option .9. $x = $array[] = array_pop($array); (due to assigning value losing original key) this option does not preserve the array's internal pointer option .5. $x = end($array); reset($array); this option is an attempt to modify option .5. to preserve the array's internal pointer (but sadly it does not scale well for very large arrays) option .6. $x = end((array_values($array))); the new array_key_last function seems to have none of the above mentioned limitations with the exception of still being an RC at the time of this writing (so use the RC or await it's release Dec 2018): option 10. $x = $array[array_key_last($array)]; (since PHP 7.3)
根据使用数组作为堆栈还是队列，你可以在选项9上做一些变化。
这里的大多数解决方案对于不关联的数组是不可靠的，因为如果我们有一个最后一个元素为false的不关联数组，那么end和current(array_slice($array， -1))也将返回false，因此我们不能使用false作为一个空的不关联数组的指示符。
// end returns false form empty arrays
>>> $arr = []
>>> end($arr)
=> false
// last element is false, so end returns false,
// now we'll have a false possitive that the array is empty
>>> $arr = [1, 2, 3, false]
>>> end($arr)
=> false
>>> $arr = [1, 2, 3, false, 4]
>>> end($arr)
=> 4
对于current(array_slice($arr， -1))也是一样:
// returns false form empty arrays
>>> $arr = []
>>> current(array_slice($arr, -1))
=> false
// returns false if last element is false
>>> $arr = [1, 2, 3, false]
>>> current(array_slice($arr, -1))
=> false
>>> $arr = [1, 2, 3, false, 4]
>>> current(array_slice($arr, -1))
=> 4
最好的选择是使用array_key_last，这适用于PHP >= 7.3.0或更老的版本，我们使用count来获取最后的索引(仅适用于未关联的数组):
// returns null for empty arrays
>>> $arr = []
>>> array_key_last($arr)
=> null
// returns last index of the array
>>> $arr = [1, 2, 3, false]
>>> array_key_last($arr)
=> 3
// returns last index of the array
>>> $arr = [1, 2, 3, false, 4]
>>> array_key_last($arr)
=> 4
对于旧版本，我们可以使用count:
>>> $arr = []
>>> if (count($arr) > 0) $arr[count($arr) - 1]
// No excecution
>>> $arr = [1, 2, 3, false]
>>> if (count($arr) > 0) $arr[count($arr) - 1]
=> false
>>> $arr = [1, 2, 3, false, 4]
>>> if (count($arr) > 0) $arr[count($arr) - 1]
=> 4
以上就是非关联数组的全部内容。如果我们确定我们有关联的数组，那么我们可以使用end。
又短又甜。
我想出了一个解决方案来删除错误信息，并保留一行程序形式和高效性能:
$lastEl = array_values(array_slice($array, -1))[0];
——之前的解决方案
$lastEl = array_pop((array_slice($array, -1)));
注意:额外的括号是为了避免PHP的严格标准:只有变量应该通过引用传递。
