Hello Perl Monks, I am practicing perl by picking up text parsing questions from StackOverflow and wrote the following script. The objective was to transpose the data from

Name^Code^Count
Name1^0029^1
Name1^0038^1
Name1^0053^1
Name2^0013^3
Name2^0018^3
Name2^0023^5
Name2^0025^1
Name2^0029^1
Name2^0038^1
Name2^0053^1
Name3^0018^1
Name3^0060^1
Name4^0018^2
Name4^0025^5
Name5^0018^2
Name5^0025^1
Name5^0060^1
[download]

to this:

Name^0013^0018^0023^0025^0029^0038^0053^0060
Name1^^^^^1^1^1^
Name2^3^3^5^1^1^1^1^
Name3^^1^^^^^^1
Name4^^2^^5^^^^
Name5^^2^^1^^^^1
[download]

Here is my attempt on the answer:

use strict;
use warnings;

my $map;
my $sep = '^';
my @flds;
my %codes;

# Loop through the lines and create hashmap

while (my $line = <DATA>) {
    chomp $line; 
    @flds = split ('\^', $line);
    next unless $.>1;
    $map->{$flds[0]}->{$flds[1]} = $flds[2] or next;
    $codes{$flds[1]}++;
}

# Print the header line

print "Name";
foreach my $k (sort keys %codes){
    print "$sep" . "$k";
}

print "\n";

# Iterate through the hash 

foreach my $k1 (sort keys %$map) {
    print $k1;
    foreach my $k2 (sort keys %codes) {
        print "$sep" and next unless defined $map->{$k1}->{$k2};
        print "$sep" . "$map->{$k1}->{$k2}";
    }
    print "\n";
}

__DATA__
Name^Code^Count
Name1^0029^1
Name1^0038^1
Name1^0053^1
Name2^0013^3
Name2^0018^3
Name2^0023^5
Name2^0025^1
Name2^0029^1
Name2^0038^1
Name2^0053^1
Name3^0018^1
Name3^0060^1
Name4^0018^2
Name4^0025^5
Name5^0018^2
Name5^0025^1
Name5^0060^1
[download]

My first question is for these two lines of code:

        print "$sep" and next unless defined $map->{$k1}->{$k2};
        print "$sep" . "$map->{$k1}->{$k2}";
[download]

If I print the hash without the first statement, I get lot of warnings since I believe due to autovivification, perl tries to create the hash for missing key and grabs something not defined. How can I write this idiomatically. In awk I could do

printf "%s%s", FS, map[name[i],value[j]]
[download]

and it will print the value if key exists and will nothing if it doesn't. My second question is, do I really have to create

$codes{$flds[1]}++
[download]

Can I use the master map hash for iterating through just names? If so what would be the best way? Lastly, any tips of improving the script would be greatly appreciated. This is only my second post and from the first post I do see me making some progress thanks to everyone over here.

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