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Creating a Matrix in perl...

Posted on 2009-04-05
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Last Modified: 2012-08-13
I'm doing a computation and that will result in 3 variable (Document name, document value, document term frequency) The values of the computation is in 3 separate variable, so I was thinking of grouping the values into an array or hash so I can sort the result of the computation by the following rules.

The highest document value and the highest term frequency.

here is a sample data

doc1, 0.002, 1
doc2, 0.012, 2
doc3, 0.032, 1

the search Martrix should be like this

doc2, 0.012, 2
doc3, 0.032, 1
doc1, 0.002, 1

How can I create a matrix in perl? or an array of array?
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Question by:Trexgreen
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5 Comments
 
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Accepted Solution

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mrjoltcola earned 500 total points
ID: 24072777
You can do it in a hash, then use sort on one of the values by providing a sort routine.


#!/usr/bin/perl
 
my %docs;
 
$docs{doc1} = { value => 0.002, freq => 1 };
$docs{doc2} = { value => 0.012, freq => 2 };
$docs{doc3} = { value => 0.032, freq => 1 };
 
print "Unsorted\n";
foreach my $doc (keys %docs) {
   print "$doc $docs{$doc}->{freq}\n";
}
 
print "Sorted\n";
foreach my $doc (sort {$docs{$b}->{freq} <=> $docs{$a}->{freq}} keys %docs) {
   print "$doc $docs{$doc}->{freq}\n";
}

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Expert Comment

by:mrjoltcola
ID: 24072783
And to change the sort column, change the expression

   $docs{$b}->{freq} <=> $docs{$a}->{freq}

to use whichever column to sort by. Note $b is before $a because you wanted descending sort.
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Author Comment

by:Trexgreen
ID: 24072836
can I sort two columns at once?

I want to have the highes freq and the value
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Author Comment

by:Trexgreen
ID: 24072852
Just found this... I guess I can use this to sort the result

http://search.cpan.org/~dcantrell/Sort-MultipleFields-1.0/lib/Sort/MultipleFields.pm
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LVL 40

Expert Comment

by:mrjoltcola
ID: 24072882
You can, it depends really on what you want. The <=> and cmp operators compare 2 values and return -1, 0 or 1. But you can write a sort function that makes it clearer.

So basically comparing the 1st column, if they are not equivalent, return the sort order just based on 1st column, but if they are equivalent, then return sort based on 2nd.

There may be an even more elegant solution to this, but this is how I would do it.

Keep in mind this is sorting on the fly. If you want to maintain a sorted datastructure with many items, you probably should sort them as you store them.
#!/usr/bin/perl
 
my %docs;
 
$docs{doc1} = { value => 0.002, freq => 1 };
$docs{doc2} = { value => 0.012, freq => 2 };
$docs{doc3} = { value => 0.032, freq => 1 };
$docs{doc4} = { value => 0.032, freq => 2 };
 
print "Unsorted\n";
foreach my $doc (keys %docs) {
   print "$doc $docs{$doc}->{value} $docs{$doc}->{freq}\n";
}
 
print "Sorted\n";
foreach my $doc (sort sort2desc keys %docs) {
   print "$doc $docs{$doc}->{value} $docs{$doc}->{freq}\n";
}
 
sub sort2desc {
   if($docs{$b}->{freq} > $docs{$a}->{freq}) {
      return 1;
   }
   elsif($docs{$b}->{freq} < $docs{$a}->{freq}) {
      return -1;
   }
   else {
      # 1st field equal, so sort by 2nd field
      return $docs{$b}->{value} <=> $docs{$a}->{value};
   }
}

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