按值和键对哈希进行排序（按顺序）

Question

我正在寻找一种很好的方法来在 Perl 中先按值排序，然后再按键排序。

示例：

 my %userids = (
  williams => "Marketing",
  smith    => "Research",
  johnson  => "Research",
  jones    => "Marketing",
  brown    => "Marketing",
  davis    => "Research"
);

输出：

Marketing: brown
Marketing: jones
Marketing: williams
Research: davis
Research: johnson
Research: smith

请注意，value 是第一个排序级别。第二个排序级别是键。知道如何以优雅且高性能的方式做到这一点吗？谢谢！

Answer 1

很好的参考： http://www.misc-perl-info.com/perl-sort.html #shv

#!/usr/bin/perl

my %userids = (
    williams => "Marketing",
    smith    => "Research",
    johnson  => "Research",
    jones    => "Marketing",
    brown    => "Marketing",
    davis    => "Research"
);

foreach (sort { ($userids{$a} cmp $userids{$b}) || ($a cmp $b) } keys %userids) 
{
    print "$_: $userids{$_}\n";
}

Answer 2

我想再添加一件事，在排序中使用 \Lequence 。

来自Perlfaq4：如何对哈希进行排序（可以选择按值而不是键）？

为了使我们的报告顺序不区分大小写，我们在双引号字符串中使用 \L 序列 使所有内容都小写。然后，sort() 块会比较小写值以确定键的放置顺序。

foreach (sort { $userids{$a} cmp $userids{$b} or "\L$a" cmp "\L$b" )  {
    print "$_: $userids{$_}\n"; 
} 

输出：

brown: Marketing
jones: Marketing
williams: Marketing
davis: Research
Johnson: Research # here 'J'ohnson, J is in uppercase(taking assumption), come as fifth record
smith: Research

2。

foreach (sort { $userids{$a} cmp $userids{$b} or $a cmp $b )  {
    print "$_: $userids{$_}\n"; 
}

输出：

brown: Marketing
jones: Marketing
williams: Marketing
Johnson: Research # here it shifted to fourth record
davis: Research
smith: Research