Question

在Python中我可以使用itertools.product()，文档中说的是＆＃34;笛卡尔积，相当于嵌套的for循环＆＃34;。

在Perl中它的等价物是什么？

Python中的一个例子：

import itertools
opts_list = [["A","B"], ["C","D","E"], ["F","G"]]
print list(itertools.product(*opts_list))

给出：

[（＆＃39; A＆＃39;，＆＃39; C＆＃39;，＆＃39; F＆＃39;），（＆＃39; A＆＃39;，＆＃39; C＆＃39; ;＆＃39; G＆＃39;），（＆＃39; A＆＃39;，＆＃39; D＆＃39;＆＃39; F＆＃39;），＆＃39; A＆＃39; ，＆＃39; D＆＃39; G＆＃39;），（＆＃39; A＆＃39;，＆＃39; E＆＃39;＆＃39; F＆＃39;），（＆＃39; A＆＃39;，＆＃39; E＆＃39;＆＃39; G＆＃39;），（＆＃39; B＆＃39;，＆＃39; C＆＃39;，＆＃39; ; F＆＃39;），（＆＃39; B＆＃39;，＆＃39; C＆＃39;，＆＃39; G＆＃39;），（＆＃39; B＆＃39;，＆＃39; D＆＃39;，＆＃39; F＆＃39;），（＆＃39; B＆＃39;，＆＃39; D＆＃39;，＆＃39; G＆＃39;），（＆＃39; B＆＃39;，＆＃39; E＆＃39;，＆＃39; F＆＃39;），（＆＃39; B＆＃39;，＆＃39; E＆＃39;，＆＃39; G＆＃39; ）]

Answer 1

我最终使用了：

use Math::Cartesian::Product;
cartesian {print "@_\n"} ["A","B"], ["C", "D", "E"], ["F", "G"];

Answer 2

我使用Algorithm::Loops＆＃39; NestedLoops。

use Algorithm::Loops qw( NestedLoops );

my $iter = NestedLoops([["A","B"], ["C","D","E"], ["F","G"]]);
while (my @items = $iter->()) {
    ...
}

Answer 3

我喜欢Set::CrossProduct：

#!/usr/bin/env perl

use strict;
use warnings;

use Set::CrossProduct;

my $it = Set::CrossProduct->new([
     ["A","B"],
     ["C","D","E"],
     ["F","G"]
]);

while (my $v = $it->get) {
    print "@$v\n";
}

Answer 4

您应该使用其他答案中引用的其中一个CPAN模块。但作为一个有趣的练习，我编写了自己的函数来返回任意数量的输入数组引用的笛卡尔积。

my $combinations = get_combinations(["A","B"], ["C","D","E"], ["F","G"]);

foreach my $combo (@$combinations) {
  print "@$combo\n";
}

sub get_combinations {
  my @arrays = @_;

  # pre-determine to the total number of combinations
  my $total = 1;
  foreach my $aref (@arrays) {
    # if our array is empty, add 1 undef item
    push(@$aref, undef) unless scalar @$aref;
    $total *= scalar @$aref;
  }

  my $matrix = [];
  my $block_size = $total;
  for (my $col = 0; $col <= $#arrays; $col++) {
    # determine the number of consecutive times to print each item in the column
    $block_size = $block_size / scalar @{$arrays[$col]};

    # fill-in our 2-D array (matrix), one column (input array) at a time
    for (my $row = 0; $row < $total; $row++) {
      my $item_index = int($row / $block_size) % scalar @{$arrays[$col]};
      $matrix->[$row]->[$col] = $arrays[$col]->[$item_index];
    }

  }

  return wantarray ? @$matrix : $matrix;
}

Python中的itertools.product（）等效于Perl

4 个答案: