sorting using substrs of same string

seaver has asked for the wisdom of the Perl Monks concerning the following question:

Dear all,

my problem lies in the fact that the interpreter seems to ignore the second section, which is are substr of the values use in the first section:

foreach my $ref ( sort { $a cmp $b 
                     || 
                     substr($a,1) <=> substr($b,1) 
                 } keys %{$self->{'residues'}{$i}}){
        print "$ref\t";
    }
[download]

The $refs are simply letters in uppercase followed by numbers, id like to sort them by their letters, and then by the numbers. Here is a sample (but wrong) output:

A95
A96
A97
A98
A99
B1
B10
B11
B12
B13
[download]

If I dont include the '$a cmp $b', then the keys are sorted according to the numbers, so I know that the substr section is working, but it just doesn't seem to pass through the '||'...

cheers
Sam

Comment on sorting using substrs of same string Select or Download Code

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Re: sorting using substrs of same string by seaver (Pilgrim) on Sep 23, 2003 at 20:25 UTC
Dear all, figured it out for myself, it was my last sentence that made me think about it more: "but it just doesn't seem to pass through the '\|\|'..." Re-reading the definition of the comparison operators, they return '0' for equivalence and the two strings being compared, though sorted, were never going to be equal, hence sort never fell through to the next level. here's my solution: `foreach my $ref ( sort { substr($a,0,1) cmp substr($b,0,1) \|\| substr($a,1) <=> substr($b,1) } keys %{$self->{'residues'}{$i}}){ print "$ref\t"; }` [download] cheers Sam	[reply] [d/l]
Re2: sorting using substrs of same string by dragonchild (Archbishop) on Sep 23, 2003 at 21:10 UTC
Cardboard Programmers are amazing, aren't they? :-) Well done. ------ We are the carpenters and bricklayers of the Information Age. The idea is a little like C++ templates, except not quite so brain-meltingly complicated. -- TheDamian, Exegesis 6 Please remember that I'm crufty and crochety. All opinions are purely mine and all code is untested, unless otherwise specified.	[reply]