在不删除数组的情况下获取数组最后一个元素的最佳方法是什么? [英] What's the best way to get the last element of an array without deleting it?

查看：74 发布时间：2020/5/26 22:26:45 php arrays

本文介绍了在不删除数组的情况下获取数组最后一个元素的最佳方法是什么?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

好吧

我完全了解 array_pop() ，但这会删除最后一个元素.在不删除数组的情况下获取数组最后一个元素的最佳方法是什么?

I know all about array_pop(), but that deletes the last element. What's the best way to get the last element of an array without deleting it?

这是一个奖励:

$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

推荐答案

此主题中的许多答案为我们提供了许多不同的选择.为了能够从他们中进行选择，我需要了解他们的行为和表现.在此答案中，我将与您分享我的发现，它们以PHP版本5.6.38，7.2.10和7.3.0RC1为基准(

The many answers in this thread present us with many different options. To be able to choose from them I needed to understand their behavior and performance. In this answer I will share my findings with you, benchmarked against PHP versions 5.6.38, 7.2.10 and 7.3.0RC1 (expected Dec 13 2018).

我要测试的选项(<<option code>> s)是:

The options (<<option code>>s) I will test are:

选项.1. $x = array_values(array_slice($array, -1))[0];(根据建议通过 rolacja )
选项.2. $x = array_slice($array, -1)[0];(根据建议通过 Stoutie )
选项.3. $x = array_pop((array_slice($array, -1)));(根据建议通过 rolacja )
选项.4. $x = array_pop((array_slice($array, -1, 1)));(根据建议通过 Westy92 )
选项.5. $x = end($array); reset($array);(根据建议通过 Iznogood )
选项.6. $x = end((array_values($array)));(根据建议通过 TecBrat )
选项.7. $x = $array[count($array)-1];(根据建议通过 Mirko Pagliai )
选项.8. $keys = array_keys($array); $x = $array[$keys[count($keys)-1]];(根据建议通过 thrau )
选项.9. $x = $array[] = array_pop($array);(中的最后一个元素不删除它/41795859#comment63556865_3687358> /user2782001> user2782001 )
选项10. $x = $array[array_key_last($array)];(根据建议通过 Quasimodo的克隆；可用于PHP 7.3)

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)

(提到的功能: array_key_last ， array_keys ， array_values ， count ，

(functions mentioned: array_key_last , array_keys , array_pop , array_slice , array_values , count , end , reset)

要与以下各项组合的测试输入(<<input code>> s)

The test inputs (<<input code>>s) to combine with:

空 = $array = null;

空 = $array = [];

last_null = $array = ["a","b","c",null];

auto_idx = $array = ["a","b","c","d"];

随机播放 = $array = []; $array[1] = "a"; $array[2] = "b"; $array[0] = "c";

100 = $array = []; for($i=0;$i<100;$i++) { $array[] = $i; }

100000 = $array = []; for($i=0;$i<100000;$i++) { $array[] = $i; }

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 = $array = []; for($i=0;$i<100000;$i++) { $array[] = $i; }

为了进行测试，我将使用5.6.38，7.2.10和7.3.0RC1 PHP docker容器，例如:

For testing I will use the 5.6.38, 7.2.10 and 7.3.0RC1 PHP docker containers like:

sudo docker run -it --rm php:5.6.38-cli-stretch php -r '<<<CODE HERE>>>'

上面列出的<<option code>>和<<input code>>的每种组合都将在所有版本的PHP上运行.对于每个测试运行，都使用以下代码片段:

Each combination of the above listed <<option code>>s and <<input code>>s will be run on all versions of PHP. For each test run the following code snippet is used:

<<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转储测试输入的最后检索到的最后一个值，并打印一次迭代的平均持续时间

For each run this will var_dump the last retrieved last value of the test input and print the average duration of one iteration in femtoseconds (0.000000000000001th of a second).

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 || \=========================================================================================================================================================================================================================================================================================================================================================================================================================/

上面提到的 F 原子， W 警告和 N 等离子码翻译为:

The above mentioned Fatal, Warning and Notice codes translate as:

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

基于此输出，我得出以下结论:

Based on this output I draw the following conclusions:

较新版本的PHP的性能更好，但以下选项却变得非常慢:

选项.6. $x = end((array_values($array)));

选项.8. $keys = array_keys($array); $x = $array[$keys[count($keys)-1]];

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]];

选项.5. $x = end($array); reset($array);

选项.7. $x = $array[count($array)-1];

选项.9. $x = $array[] = array_pop($array);

选项10. $x = $array[array_key_last($array)];(自PHP 7.3起)

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)

选项.7. $x = $array[count($array)-1];(由于使用count)

选项.9. $x = $array[] = array_pop($array);(由于分配了丢失原始密钥的值)

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)

选项.5. $x = end($array); reset($array);

选项.6. $x = end((array_values($array)));

选项10. $x = $array[array_key_last($array)];(自PHP 7.3起)

option 10. $x = $array[array_key_last($array)]; (since PHP 7.3)

根据是否使用数组作为堆栈或队列，您可以对选项9进行更改.

A bit depending on whether using the array as stack or as queue you can make variations on option 9.

这篇关于在不删除数组的情况下获取数组最后一个元素的最佳方法是什么?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

查看全文

在不删除数组的情况下获取数组最后一个元素的最佳方法是什么? [英] What's the best way to get the last element of an array without deleting it?

问题描述

推荐答案

相关文章

PHP最新文章

热门教程

热门工具

登录关闭

在不删除数组的情况下获取数组最后一个元素的最佳方法是什么? [英] What&#39;s the best way to get the last element of an array without deleting it?

问题描述

推荐答案

相关文章

PHP最新文章

热门教程

热门工具

登录 关闭

在不删除数组的情况下获取数组最后一个元素的最佳方法是什么? [英] What's the best way to get the last element of an array without deleting it?

登录关闭