Re^4: top ten things every Perl hacker should know

[Your Mother]

It's all right in front of you; in one sweep of your eye. The filtering, the modification, and the sorting (grep, map, sort, and maybe more). There aren't a couple sets of temporary variables and three or more bocks or subroutines to jump around and try to keep in your head at once. It's the same code condensed. I find it easier to read and much easier to debug.

So I do think the ST is a good example of elegance. I'm open to counter examples of what you consider Perl (not Python or Ruby of course!) elegance.

[tilly]

Let's take a list of files and use a Schwartzian Transform to sort it by file size descending, then alphabetical order ascending.

my @sorted_files
  = map {$_->[0]}
    sort {$b->[1] <=> $a->[1] or $a->[0] cmp $b->[0]}
    map {[$_, -s]} @files;

Here is the same code written as a normal sort.

my @sorted_files = sort {-s $b <=> -s $a or $a cmp $b} @files;

Clearly the Schwartzian Transform is more complex. But if you have a list of 1000 files, it's also about 10 times faster. Which is why we learn it.

Now to explain my Ruby comment. In Ruby, arrays have a sort_by method. So in this example you'd write:

sorted_files = files.sort_by {|f| [- test(?s, f), f]};

and you've written the more efficient sort with less code than the regular sort. This does not work in Perl first of all because we don't have a sort_by method, and furthermore because Perl doesn't do anything useful when you try to sort array references. (Ruby sorts them lexicographically, with each field sorting in its "natural" way.)

[qq]

We sort of have a sort_by method in Sort::Maker. But I've never liked the api. There is no denying that an ST is a scary sight to a new programmer not familiar with the idiom. I'd argue it should be wrapped in a sub for clarity most often.

I like the PBP argument for using List::Util and List::MoreUtils functions such as any rather than idiomatic uses of grep. It makes your intention clear, and prevents you from thinking in syntax - no matter how comfortable and familiar that syntax is.

update: added some words for clarity

[salva]

We sort of have a sort_by method in Sort::Maker. But I've never liked the api

you should try Sort::Key, it has a very simple API and it's faster and uses less memory than any other perl sorting technique:

use Sort::Key qw(keysort);
my @sorted = keysort { genkey($_) } @data;