Hi PerlMonks people!

I have a rather tricky sort question that I've been trying to solve. In my array of hashes I've ID, Distance and RouteDistance. I want to sort on RouteDistance but this value is sometimes 0 and here comes the tricky part. When RouteDistance is 0 I want the sorting to be done on the Distance for this hash instead.

This example might make my problem clearer:

ID = 3, Distance = 2.3, RouteDistance = 4.3
ID = 2, Distance = 1.5, RouteDistance = 2.8
ID = 5, Distance = 2.1, RouteDistance = 0
ID = 1, Distance = 1.7, RouteDistance = 2.5

I want the sorting to be presented as this when the sorting is done:

ID = 1, Distance = 1.7, RouteDistance = 2.5
ID = 2, Distance = 1.5, RouteDistance = 2.8
ID = 5, Distance = 2.1, RouteDistance = 0
ID = 3, Distance = 2.3, RouteDistance = 4.3

Example code that I've been trying to make this work with...

From an XMLpost I'm receiving an array of hash references which im calling $xml_post_array{'data'}

In this first example I manage to sort by RouteDistance and in cases where RouteDistance is equal with another RouteDistance it will sort by Distance.

my @unsortedArray;
foreach my $received_xml_post (@ {$xml_post_array{'data'}})
{
           push @unsortedArray, {
                                'ID' => $received_xml_post->{'ID'},
                                'Distance => $received_xml_post->{'Dis
+tance'},
                                'RouteDistance' => $received_xml_post-
+>{'RouteDistance'}};
}

my @sortedArray = sort { $a->{RouteDistance} <=> $b->{RouteDistance ||
+ $a->{Distance} <=> $b->{Distance} } @unsortedArray;
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In the next example I want to get around the RouteDistance cases where RouteDistance is equal to 0.

my @unsortedArray;
foreach my $received_xml_post (@ {$xml_post_array{'data'}})
{
   push @unsortedArray, {
                         'ID' => $received_xml_post->{'ID'},
                         'Distance => $received_xml_post->{'Distance'}
+,
                         'RouteDistance' => $received_xml_post->{'Rout
+eDistance'}};
}

my @sortedArray = sort { if( $a->{RouteDistance} == 0) {return -1} els
+e {$a->{RouteDistance} <=> $b->{RouteDistance} $a->{Distance} <=> $b-
+>{Distance} } @unsortedArray;
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The 2nd code example will just sort everything on Distance. I've done an ugly version of this sorting that first sorts on Distance. Then I loop trough this and save current RouteDistance and in cases where RouteDinstance is equal to 0 I just pick up that previous RouteDistance and add 0.001 to it. However, this solution does not work with exreame cases and therefore I want to find out if there is a better way to handle this type of sorting. I'm sorry in advance for my English (not my native language). This is my first post here by the way so I might have done something wrong with this post but just let me know and I will now to next time.

Update 1: One of the suggestions that was close to achiveing this was this peace of code:

sort {
    $a->{routedistance} && $b->{routedistance} 
    ? $a->{routedistance} <=> $b->{routedistance}
    : $a->{distance} <=> $b->{distance}
} @ar;
[download]

unfortunately, this turned out to not work as I wanted when the RouteDistance was pre-ordered where one of the RouteDistance was zero.

I can add one thing to the table. The value of RouteDistance is not important, as long as it is sorted as I've described above. What I mean by this is that cases where RouteDistance is zero, this value can be replaces to something else, for example previous RouteDistance or nearest + 0.01 / -0.01. The value of RouteDistance will not be used to anything else then just sorting which makes this one option.

Update 2: The problem is not yet solved and and have no good solution for it.. :/

Update 3: The problem is solved. It might be some extreme cases where this all falls apart but with the tests I've done it works.

The solution:

#!/usr/bin/perl
use warnings;
use strict;

my @unsorted_array = (    { ID => 3, Distance => 2.3, RouteDistance =>
+ 4.3 },
                        { ID => 2, Distance => 1.5, RouteDistance => 2
+.8 },
                        { ID => 5, Distance => 2.1, RouteDistance => 0
+ },
                        { ID => 1, Distance => 1.7, RouteDistance => 2
+.5 });

my @sorted = sort { 
    if($a->{RouteDistance} == 0 || $b->{RouteDistance} == 0)
    {
        return ($a->{Distance} < $b->{Distance}) ? -1 : 1;
    }
    elsif ($a->{RouteDistance} == $b->{RouteDistance})
    {    
        return 0;
    }
    else
    {
        return ($a->{RouteDistance} < $b->{RouteDistance}) ? -1 : 1;
    }
} @unsorted_array;


foreach my $sorted_row (@sorted)
{
    print "ID: ".$sorted_row->{'ID'}." Distance: ".$sorted_row->{'Dist
+ance'}." RouteDistance: ".$sorted_row->{'RouteDistance'}."\n";
}
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