如何将@{$subset}，[@ext_subset]，[$last_item]放在PHP中？

Question

我在将子例程从Perl转换为PHP时遇到了问题(我是Perl新手)。整个子例程如下：

sub find_all_subsets {
  if (1 == scalar (@_)) {return [@_]}
  else {
    my @all_subsets = () ;
    my $last_item = pop (@_) ;
    my @first_subsets = find_all_subsets (@_) ;
    foreach my $subset (@first_subsets) {
      push (@all_subsets, $subset) ;
      my @ext_subset = @{$subset} ;
      push (@ext_subset, $last_item) ;
      push (@all_subsets, [@ext_subset]) ;
    }
    push (@all_subsets, [$last_item]) ;
    return (@all_subsets) ;
  }
}

我的问题是我真的不太了解Perl语法，所以我在用PHP编写这些@{$subset}、[@ext_subset]和[$last_item]时遇到了麻烦。

谢谢，如果这个问题很愚蠢，我很抱歉。

Answer 1

当我跑的时候

use Data::Dumper;
$Data::Dumper::Terse = 1;
$Data::Dumper::Indent = 0; 
my @x = (1,2,3,4);
my @y = find_all_subsets(@x);
foreach my $subset (@y) {
  print Dumper($subset), "\n";
}

(+原始脚本)输出是

[1]
[1,4]
[1,3]
[1,3,4]
[1,2]
[1,2,4]
[1,2,3]
[1,2,3,4]
[2]
[2,4]
[2,3]
[2,3,4]
[3]
[3,4]
[4]

请注意输出中的，我们稍后再讨论它们。

function find_all_subsets (array $x) {
  if ( 1>= count($x) ) { // the >= differs from the original script, use == or === if you want to keep it "more original"
    return array($x);
  } 
  else {
    $all_subsets = array();
    $last_item = array_pop($x);
    $first_subsets = find_all_subsets($x) ;
    foreach ($first_subsets as $subset) {
      array_push($all_subsets, $subset);
      array_push($subset, $last_item);
      array_push($all_subsets, $subset);
    }
    array_push ($all_subsets, array($last_item));
    return $all_subsets;
  }
}

$x = array(1,2,3,4);
$y = find_all_subsets($x);
foreach($y as $subset) {
  echo '(', join(',', $subset), ")\n";
}

产生

(1)
(1,4)
(1,3)
(1,3,4)
(1,2)
(1,2,4)
(1,2,3)
(1,2,3,4)
(2)
(2,4)
(2,3)
(2,3,4)
(3)
(3,4)
(4)

到目前一切尚好。现在回到。Dumper之所以选择这个而不是()，是因为它不是一个数组，而是一个数组引用(如果我没有使用正确的术语，就直接告诉我吧；perl确实不是我的强项)。让我们更改perl测试脚本并查看所有这些引用内容所具有的效果。

use Data::Dumper;
$Data::Dumper::Terse = 1;
$Data::Dumper::Indent = 0; 
$x2 = 2;
my @x = (1,\$x2,3,4);
my @y = find_all_subsets(@x);
$x2 = 99;
foreach my $subset (@y) {
  print Dumper($subset), "\n";
}

并将输出更改为

[1]
[1,4]
[1,3]
[1,3,4]
[1,\99]
[1,\99,4]
[1,\99,3]
[1,\99,3,4]
[\99]
[\99,4]
[\99,3]
[\99,3,4]
[3]
[3,4]
[4]

您看，我在调用find_all_subsets()之后更改了$x2，但在结果中仍然使用了新值，Data::Dumper将" value“标记为引用( \99而不是简单的99 )。你的php脚本中也需要这个功能吗？

Answer 2

[]是一个数组引用运算符，用于将数组转换为数组引用

@{}是一个数组取消引用运算符，它将数组引用转换为数组

@a = (1,2,3);
$a = [ @a ];
@b = @{$a};       # now @b ==> (1,2,3)

Answer 3

如下所示：

@{$subset}    # Return array reference as an ordinary array, not applicable in PHP.
[@ext_subset] # Turn an array into an array reference, not applicable in PHP.
[$last_item]  # Create an array with $last_item as the only element, equal to array($last_item) in PHP.