I suspect the error you listed is occurring because there is a gap in the array that you created. As in this example: 
use Data::Dumper;
my @array = ();
$array[0] = [1];
$array[2] = [2];
@array = sort { $$a[0] cmp $$b[0]} @array;
print Dumper \@array;

[download]
As for the sorting algorithm, the most common approach would be something like this: 
use strict;
use warnings;
use Data::Dumper;

my @courselist = ( 
    ["UM", "CS 34", ],
    ["AC", "PHIL 13", ],
    ["UM", 'BIO 567', ],
    ["UA", 'BIO 999', ],
    ["UM", 'BIO 1', ],
);  


@courselist = sort {$$a[0] cmp $$b[0] or $$a[1] cmp $$b[1]} @courselis
+t;
print Dumper(\@courselist);

[download]
As for the problem you are solving, it would probably be faster and easier to handle the sorting in a database, where the book information should probably be stored. Good luck with the project, I'll stop by your store next time I'm in Amherst :)

In reply to Re: sorting an array of an arrays by imp
in thread sorting an array of an arrays by Gnat53

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