Re^3: Hash sorting (by value) woes

Here's an optmization that only executes the regexp once per string:

@sorted_keys = map { $_->[0] }
               sort { $a->[1] <=> $b->[1] }
               map { $etcpw->{$_} =~ /:(\d+)/; [ $_, $1 ] }
               keys %{$etcpw};

print "$etcpw->{$_}\n"
   foreach @sorted_keys;
[download]

We can even drop a step:

print "$etcpw->{$_->[0]}\n"
   foreach
      sort { $a->[1] <=> $b->[1] }
      map { $etcpw->{$_} =~ /:(\d+)/; [ $_, $1 ] }
      keys %{$etcpw};
[download]

Comment on Re^3: Hash sorting (by value) woes Select or Download Code

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Re^4: Hash sorting (by value) woes by Roy Johnson (Monsignor) on Feb 24, 2005 at 17:33 UTC
Of course, if you really want to use map instead of foreach: `print map {"$etcpw->{$_}\n"} sort { $a->[1] <=> $b->[1] } map { $etcpw->{$_} =~ /:(\d+)/; [ $_, $1 ] } keys %{$etcpw};` [download] Caution: Contents may have been coded under pressure.	[reply] [d/l]
Re^5: Hash sorting (by value) woes by ikegami (Patriarch) on Feb 24, 2005 at 17:42 UTC
True, but it would be slower. `print map { ...1... } ...2...;` [download] is closer to `@temp_list = map { ...1... } ...2...; print @temp_list;` [download] than to `print ...1... foreach ...2...;` [download] The extra assignment slows things down. (About twice as slow, IIRC previous tests.) Update: Fixed brain fart R.J. noticed.	[reply] [d/l] [select]
Re^6: Hash sorting (by value) woes by Roy Johnson (Monsignor) on Feb 24, 2005 at 18:03 UTC
Isn't it more like `@temp_list = map { ...1... } ...2....; print @temp_list;` [download] ? The map is done before print sees it, and print is only called once, with a list. It is slower, of course, because you do have an extra list-building step. Interestingly, it is not slower than map in a void context (I'm using 5.8.0 here -- when was that optimized?): `use Benchmark 'cmpthese'; my @vals = (10_000..15_000); open(ABYSS, '>', '/dev/null') or die "The abyss is closed.\n"; cmpthese(-2, { 'map' => sub { print ABYSS map {">>$_<<\n"} @vals }, 'map_void' => sub { map {print ABYSS ">>$_<<\n"} @vals }, 'for' => sub { print ABYSS ">>$_<<\n" for @vals } }); close ABYSS; __END__ Rate map_void map for map_void 11.9/s -- -23% -50% map 15.5/s 30% -- -34% for 23.6/s 99% 52% --` [download] Caution: Contents may have been coded under pressure.	[reply] [d/l] [select]