[B]Perl sort quick question[/B]

zx1106 · #1 (**permalink**) 10-09-2008

I've done a quick Google about this, but could not find the answer I want.

Say, there is an array like this:
@A = qw(cd1 a1 ef a2 hij a12 b2 b4 b22);

I want to sort the array in the first order:
@sorted = qw(a1 a12 a2 b2 b22 b4 cd1 ef hij);

And second order:
@sorted = qw(a1 a2 a12 b2 b4 b22 cd1 ef hij);

Is there a way to do this in Perl without using modules?

Thanks a lot!

jim mcnamara · #2 (**permalink**) 10-09-2008

Do you consider the sort function a module?

Code:

@sorted=sort(@A);

zx1106 · #3 (**permalink**) 10-09-2008

Thanks! It works for the first order.

zx1106 · #4 (**permalink**) 10-09-2008

What about the second order:
qw(a1 a2 a12 b2 b4 b22 cd1 ef hij);
Thanks!

cbkihong · #5 (**permalink**) 10-09-2008

Yes, you can sort with a custom rule. But what exactly is the rule for the sort? If you cannot work out a formal specification of the sort, no one will be able to do it "correctly".

The following gives the same ordering as you mentioned, but there is no guarantee that it is going to give you the "correct" ordering (as you might expect) for other input values:

Code:

use Data::Dumper;

@A = qw(cd1 a1 ef a2 hij a12 b2 b4 b22);
print Dumper([sort {
	my ($_a, $_b);
	for ([$a, \$_a], [$b, \$_b]) {
		$_->[0] =~ /^(.+?)(\d*)$/;
		${$_->[1]} = [$1, $2];
	}
	($$_a[0] cmp $$_b[0]) || ($$_a[1] <=> $$_b[1]);
} @A]);

KevinADC · #6 (**permalink**) 10-10-2008

Second order which appears to be first sort by alpha then digit:

Code:

my @A = qw(cd1 a1 ef a2 hij a12 b2 b4 b22);

my @sorted = map{$_->[2]}
          sort{$a->[0] cmp $b->[0] || $a->[1] <=> $b->[1]}
          map{/([a-z]*)(\d*)/;[$1,$2,$_]} @A;

print "$_\n" for @sorted;

Google "Schwartzian Transform" if interested in the cached key sort technique.

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