DrZed
User
Jun 4, 2000, 3:34 PM
Post #2 of 6
(241 views)
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Sure. How are your strings stored?
Anyway, here are all sorts of ways to sort:
If you have an array of strings:
@colors = ("red", "blue", "white", "black", "green");
@sorted = sort @colors;
#Now, @sorted is a sorted versions of @colors
Note that capitals precede lowercase and numbers would not sort properly (e.g. 100 would come before 20).
However, sort supports the passing of a subroutine to customize how it sorts.
Here's a program that sorts numbers:
#!/usr/bin/perl -w
@prices = (99,10000,209,21,901);
sub numerically { $a <=> $b }
@sorted = sort numerically @prices;
# @sorted is now a 'numerically' sorted copy of @prices
Ok, there are a few things you need to know.
One, sort passes values to be tested to the routine as $a and $b (not as part of @_). Therefore, the routine needs to compare $a and $b and return a value based on their relative order.
If $a should appear before $b, the routine should return a negative value. If $b should be before $a, then it should return a positive value. If it doesn't matter, then it should return 0.
Ok, now what's with the $a <=> $b? Well, the <=> operator compares two numbers and returns either 1, 0 or -1 depending on if the first value is greater, equal or lesser.
It could just as well have been:
sub numerically { $a-$b }
You can use cmp instead of <=> for sorting text. For example:
sub alphabetically { $a cmp $b }
Or, if you want to ignore case....
sub alphabetically { lc($a) cmp lc($b) }
That's fine for arrays. However, if you want to sort a hash (well, not sort it, but access it as if it were sorted), you can use the following:
to access the keys in alphabetical order:
foreach $key (sort keys %hash) { print $key; }
to access the values in alphabetical order:
foreach $key (sort byvalue keys %hash) { print $key; }
Enjoy,
Dr. Zed
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