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
避免引用传递错误的一种方法(例如。"end(array_values($foo))")是使用call_user_func或call_user_func_array:
// PHP Fatal error: Only variables can be passed by reference
// No output (500 server error)
var_dump(end(array(1, 2, 3)));
// No errors, but modifies the array's internal pointer
// Outputs "int(3)"
var_dump(call_user_func('end', array(1, 2, 3)));
// PHP Strict standards: Only variables should be passed by reference
// Outputs "int(3)"
var_dump(end(array_values(array(1, 2, 3))));
// No errors, doesn't change the array
// Outputs "int(3)"
var_dump(call_user_func('end', array_values(array(1, 2, 3))));
其他回答
在几乎每一种带有数组的语言中，使用A[A.size-1]都不会出错。我想不出一个基于1的数组(而不是基于0的数组)的语言例子。
如果你想让数组的最后一个元素在它的数组的循环中呢?
下面的代码将导致一个无限循环:
foreach ($array as $item) {
$last_element = end($array);
reset($array);
if ($last_element == $item) {
// something useful here
}
}
对于非关联数组，解决方案显然很简单:
$last_element = $array[sizeof ($array) - 1];
foreach ($array as $key => $item) {
if ($last_element == $item) {
// something useful here
}
}
$lastValue = end(array_values($array))
不修改$array指针。这就避免了
reset($array)
这在某些情况下可能并不理想。
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。
对我来说:
$last = $array[count($array) - 1];
associatives:
$last =array_values($array)[count($array - 1)]
