in reply to Sorting records on a single field

Hi! I don't have extensive experience with sorting methods, but in this case I think a simple approach would work, like that: 

use strict;
use warnings;

my $Line;           # one input line
my @SortedData;     # resulting sorted data set

# data set example
my @Data    =   (
                    '100644:MWTP_CAT:12002: SERVER:pid=14520:Execution
+ time:TPR015-10:(millisec):53',
                    '100644:MWTP_CAT:12002: SERVER:pid=15866:Execution
+ time:TPR015-10:(millisec):10',
                    '100644:MWTP_CAT:12002: SERVER:pid=15866:Execution
+ time:TPR015-10:(millisec):33',
                    '100644:MWTP_CAT:12002: SERVER:pid=16565:Execution
+ time:TPR007-12:(millisec):437',
                    '100644:MWTP_CAT:12002: SERVER:pid=16565:Execution
+ time:TPR007-12:(millisec):470',
                    '100644:MWTP_CAT:12002: SERVER:pid=16048:Execution
+ time:TPR009-30:(millisec):24',
                    '100644:MWTP_CAT:12002: SERVER:pid=15866:Execution
+ time:TPR012-01E:(millisec):63',
                    '100644:MWTP_CAT:12002: SERVER:pid=10427:Execution
+ time:ISCST044:(millisec):0',
                    '100644:MWTP_CAT:12002: SERVER:pid=15866:Execution
+ time:TPR012-01E:(millisec):85',
                    '100644:MWTP_CAT:12002: SERVER:pid=10428:Execution
+ time:01201E:(millisec):3',
                );

# create sorted data set
@SortedData = reverse sort { (split (/:/, $a))[-1] <=> (split (/:/, $b
+))[-1] } @Data;

### DEBUG: print input and output sets ###
print "Data Set is:\n", join ("\n", @Data), "\n";
print "Sorted Data is:\n", join ("\n", @SortedData), "\n";

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Re^2: Sorting records on a single field
by salva (Canon) on Jan 21, 2010 at 10:40 UTC
    You can get rid of the reverse operation just inverting the order of the comparison operands. In other words, instead of reverse sort { $a <=> $b } @data use sort { $b <=> $a } @data.

    In OP case: 

    @SortedData = sort { (split (/:/, $b))[-1] <=> (split (/:/, $a))[-1] }
+ @Data;

    [download]

    Using reverse also makes the sort operation unstable (entries with equal sorting keys do not keep their relative positions after the sort operation).

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      I see that switching the opereands is better but I don't catch what you mean with "equal sorting keys do not keep their relative positions after the sort operation"... probably I miss something. Could you explain deeply that point? Thanks.

[reply]
        Sure! Let me do it with an example: 
        my @data = qw(1a 1b 2a 2b);
my @s1 = reverse sort { $a <=> $b } @data;
my @s2 = sort { $b <=> $a } @data;
print "@s1\n@s2\n";

        [download]
        generates: 
        2b 2a 1b 1a
2a 2b 1a 1b

        [download]
        Note how in the second row, elements with the same sorting key (the numeric part) appear in the same order they had in @data while in the first row, corresponding to the reverse solution, they do not.
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