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Need perl help

Posted on 2014-01-04
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Last Modified: 2014-01-05
Hi ,
I am learning perl and i cant able to find the logic to get it worked.

Input
1,AC10308120AC1030812A.jpg
1,AC10308120AC1030812B.JPG
1,AC1030812AC1030812A.jpg
2,BA037BA037.jpg
2,BBF03BBF03A.jpg
3,BBYF03BBYF03A.jpg

Output needed:
1,AC10308120AC1030812A.jpg,AC10308120AC1030812B.JPG,AC1030812AC1030812A.jpg
2,BA037BA037.jpg,BBF03BBF03A.jpg
3,BBYF03BBYF03A.jpg
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Question by:magento
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5 Comments
 
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Accepted Solution

by:
wilcoxon earned 1800 total points
ID: 39756178
use strict;
use warnings;
my %data;
while (<>) {
    chomp;
    my ($num, $fil) = split /,/;
    $data{$num} = [] unless exists($data{$num});
    push @{$data{$num}}, $fil;
}
foreach my $num (sort { $a <=> $b } keys %data) {
    print "$num,", join(',', @{$data{$num}}), "\n";
}

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Author Comment

by:magento
ID: 39756197
Hi Wilcoxon,

Works like charm ..

Can you please add few comments on the below so i can learn it.


my ($num, $fil) = split ",";

So the above line will split using comma and place the key value respectively
so i get $num=1 and $fil=image1.jpg for 1st line

push @{$data{$num}}, $fil;

so here we push the $fil to the array and we have

@array = (1,image.jpg);

Am i right, i dont understand this part , please clarify

Thanks
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LVL 27

Expert Comment

by:wilcoxon
ID: 39756254
split uses a regex (hence /,/ instead of ',').  Yes, split will split the value ($_ by default) using the regex provided into a list.  Since there are only two values per line, I prefer to enumerate each (the general form would be @list = split /,/).

Not quite.  %data is a hash so $data{$num} is an element of the hash (in this case $data{1}).  Push adds the value ($fil) to the array (which in this case is really the arrayref $data{1}).  So what we really have is $data{1} = [image.jpg].
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Assisted Solution

by:ozo
ozo earned 200 total points
ID: 39756516
$data{$num} = [] unless exists($data{$num}); # is uneccessary.  It would be autovivified by the push

split ","; # is the same as split /,/;  # although split " "; is not the same as split / /;
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LVL 27

Expert Comment

by:wilcoxon
ID: 39756536
I never remember which actions autovivify so I usually default on the safe side.

The differences in behavior for some values is why I always use regex syntax for split (plus that's what the perldoc suggests for syntax).
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