foreach的性能,带有lambda的array_map和带有静态函数的array_map

Question

这三种方法之间的性能差异(如果有的话)是什么,都用于将数组转换为另一个数组？

1. 运用 foreach
2. 使用array_maplambda/closure函数
3. 使用array_map'静态'功能/方法
4. 还有其他方法吗？

为了使自己清楚,让我们看看这些例子,都做同样的事情 - 将数字数组乘以10:

$numbers = range(0, 1000);

---

的foreach

$result = array();
foreach ($numbers as $number) {
    $result[] = $number * 10;
}
return $result;

---

用lambda映射

return array_map(function($number) {
    return $number * 10;
}, $numbers);

---

使用'static'函数映射,作为字符串引用传递

function tenTimes($number) {
    return $number * 10;
}
return array_map('tenTimes', $numbers);

---

还有其他方法吗？我将很高兴听到上述案例之间的所有差异,以及为什么应该使用其他人而不是其他人的任何输入.

Answer 1

由于xdebug增加了很多开销,尤其是函数调用,因此在禁用xdebug的情况下运行此基准测试很有意思.

这是使用5.6 With xdebug运行的FGM脚本

ForEach   : 0.79232501983643
MapClosure: 4.1082420349121
MapNamed  : 1.7884571552277

没有xdebug

ForEach   : 0.69830799102783
MapClosure: 0.78584599494934
MapNamed  : 0.85125398635864

这里foreach和closure版本之间只有很小的差别.

添加带有闭包的版本也很有趣 use

function useMapClosureI($numbers) {
  $i = 10;
  return array_map(function($number) use ($i) {
      return $number * $i++;
  }, $numbers);
}

为了比较,我添加:

function useForEachI($numbers)  {
  $result = array();
  $i = 10;
  foreach ($numbers as $number) {
    $result[] = $number * $i++;
  }
  return $result;
}

在这里我们可以看到它对闭包版本产生了影响,而数组没有明显改变.

19/11/2015我现在还使用PHP 7和HHVM添加结果进行比较.虽然一切都快得多,但结论却相似.

PHP 5.6

ForEach    : 0.57499806880951
MapClosure : 0.59327731132507
MapNamed   : 0.69694859981537
MapClosureI: 0.73265469074249
ForEachI   : 0.60068697929382

PHP 7

ForEach    : 0.11297199726105
MapClosure : 0.16404168605804
MapNamed   : 0.11067249774933
MapClosureI: 0.19481580257416
ForEachI   : 0.10989861488342

HHVM

ForEach    : 0.090071058273315
MapClosure : 0.10432276725769
MapNamed   : 0.1091267824173
MapClosureI: 0.11197068691254
ForEachI   : 0.092114186286926

Answer 2

FWIW,我刚刚做了基准,因为海报没有这样做.在PHP 5.3.10 + XDebug上运行.

更新2015-01-22与mcfedr的答案进行比较,以获得没有XDebug和更新的PHP版本的其他结果.

function lap($func) {
  $t0 = microtime(1);
  $numbers = range(0, 1000000);
  $ret = $func($numbers);
  $t1 = microtime(1);
  return array($t1 - $t0, $ret);
}

function useForeach($numbers)  {
  $result = array();
  foreach ($numbers as $number) {
      $result[] = $number * 10;
  }
  return $result;
}

function useMapClosure($numbers) {
  return array_map(function($number) {
      return $number * 10;
  }, $numbers);
}

function _tenTimes($number) {
    return $number * 10;
}

function useMapNamed($numbers) {
  return array_map('_tenTimes', $numbers);
}

foreach (array('Foreach', 'MapClosure', 'MapNamed') as $callback) {
  list($delay,) = lap("use$callback");
  echo "$callback: $delay\n";
}

在十几次尝试中,我获得了非常一致的结果,包括1M数字:

• Foreach:0.7秒
• 关闭地图:3.4秒
• 功能名称上的映射:1.2秒.

假设关闭时地图的速度低迷是因为关闭可能每次都被评估,我也测试过这样:

function useMapClosure($numbers) {
  $closure = function($number) {
    return $number * 10;
  };

  return array_map($closure, $numbers);
}

但结果是相同的,证实封闭只评估一次.

2014-02-02更新:操作码转储

以下是三个回调的操作码转储.第一useForeach():

compiled vars:  !0 = $numbers, !1 = $result, !2 = $number
line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
  10     0  >   EXT_NOP                                                  
         1      RECV                                                     1
  11     2      EXT_STMT                                                 
         3      INIT_ARRAY                                       ~0      
         4      ASSIGN                                                   !1, ~0
  12     5      EXT_STMT                                                 
         6    > FE_RESET                                         $2      !0, ->15
         7  > > FE_FETCH                                         $3      $2, ->15
         8  >   OP_DATA                                                  
         9      ASSIGN                                                   !2, $3
  13    10      EXT_STMT                                                 
        11      MUL                                              ~6      !2, 10
        12      ASSIGN_DIM                                               !1
        13      OP_DATA                                                  ~6, $7
  14    14    > JMP                                                      ->7
        15  >   SWITCH_FREE                                              $2
  15    16      EXT_STMT                                                 
        17    > RETURN                                                   !1
  16    18*     EXT_STMT                                                 
        19*   > RETURN                                                   null

那么 useMapClosure()

compiled vars:  !0 = $numbers
line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
  18     0  >   EXT_NOP                                                  
         1      RECV                                                     1
  19     2      EXT_STMT                                                 
         3      EXT_FCALL_BEGIN                                          
         4      DECLARE_LAMBDA_FUNCTION                                  '%00%7Bclosure%7D%2Ftmp%2Flap.php0x7f7fc1424173'
  21     5      SEND_VAL                                                 ~0
         6      SEND_VAR                                                 !0
         7      DO_FCALL                                      2  $1      'array_map'
         8      EXT_FCALL_END                                            
         9    > RETURN                                                   $1
  22    10*     EXT_STMT                                                 
        11*   > RETURN                                                   null

它调用的闭包:

compiled vars:  !0 = $number
line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
  19     0  >   EXT_NOP                                                  
         1      RECV                                                     1
  20     2      EXT_STMT                                                 
         3      MUL                                              ~0      !0, 10
         4    > RETURN                                                   ~0
  21     5*     EXT_STMT                                                 
         6*   > RETURN                                                   null

那么useMapNamed()功能:

compiled vars:  !0 = $numbers
line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
  28     0  >   EXT_NOP                                                  
         1      RECV                                                     1
  29     2      EXT_STMT                                                 
         3      EXT_FCALL_BEGIN                                          
         4      SEND_VAL                                                 '_tenTimes'
         5      SEND_VAR                                                 !0
         6      DO_FCALL                                      2  $0      'array_map'
         7      EXT_FCALL_END                                            
         8    > RETURN                                                   $0
  30     9*     EXT_STMT                                                 
        10*   > RETURN                                                   null

以及它调用的命名函数_tenTimes():

compiled vars:  !0 = $number
line     # *  op                           fetch          ext  return  operands
---------------------------------------------------------------------------------
  24     0  >   EXT_NOP                                                  
         1      RECV                                                     1
  25     2      EXT_STMT                                                 
         3      MUL                                              ~0      !0, 10
         4    > RETURN                                                   ~0
  26     5*     EXT_STMT                                                 
         6*   > RETURN                                                   null

Answer 3

以下是当前 PHP 8 (RC2) 版本的一些更新测试。还添加了短闭合

PHP 8.0 RC2

Foreach:         0.093745978673299
MapClosure:      0.096948345502218
MapShortClosure: 0.096264243125916
MapNamed:        0.091399153073629
MapClosureI:     0.11352666219076
ForEachI:        0.097501540184021

Answer 4

这真有趣.但是我从以下代码得到了相反的结果,这些代码从我当前的项目中简化了:

// test a simple array_map in the real world.
function test_array_map($data){
    return array_map(function($row){
        return array(
            'productId' => $row['id'] + 1,
            'productName' => $row['name'],
            'desc' => $row['remark']
        );
    }, $data);
}

// Another with local variable $i
function test_array_map_use_local($data){
    $i = 0;
    return array_map(function($row) use ($i) {
        $i++;
        return array(
            'productId' => $row['id'] + $i,
            'productName' => $row['name'],
            'desc' => $row['remark']
        );
    }, $data);
}

// test a simple foreach in the real world
function test_foreach($data){
    $result = array();
    foreach ($data as $row) {
        $tmp = array();
        $tmp['productId'] = $row['id'] + 1;
        $tmp['productName'] = $row['name'];
        $tmp['desc'] = $row['remark'];
        $result[] = $tmp;
    }
    return $result;
}

// Another with local variable $i
function test_foreach_use_local($data){
    $result = array();
    $i = 0;
    foreach ($data as $row) {
        $i++;
        $tmp = array();
        $tmp['productId'] = $row['id'] + $i;
        $tmp['productName'] = $row['name'];
        $tmp['desc'] = $row['remark'];
        $result[] = $tmp;
    }
    return $result;
}

这是我的测试数据和代码:

$data = array_fill(0, 10000, array(
    'id' => 1,
    'name' => 'test',
    'remark' => 'ok'
));

$tests = array(
    'array_map' => array(),
    'foreach' => array(),
    'array_map_use_local' => array(),
    'foreach_use_local' => array(),
);

for ($i = 0; $i < 100; $i++){
    foreach ($tests as $testName => &$records) {
        $start = microtime(true);
        call_user_func("test_$testName", $data);
        $delta = microtime(true) - $start;
        $records[] = $delta;
    }
}

// output result:
foreach ($tests as $name => &$records) {
    printf('%.4f : %s '.PHP_EOL, 
              array_sum($records) / count($records), $name);
}

结果是:

0.0098 : array_map
0.0114 : foreach
0.0114 : array_map_use_local
0.0115 : foreach_use_local

我的测试是在没有xdebug的LAMP生产环境中进行的.我徘徊xdebug会降低array_map的性能.