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### test1.csv ###
1  aaa  ignored_field
...
555 eee ignored_field
666  fff   ignored_field
777  ggg   ignored_field

#!/usr/bin/perl
use v5.14;
...
for my $key (sort keys %data) {
    say "$key\t$data{$key}";
}

$ ./report.pl 
Key    f1    f2    f3
...
eee    0    0    555    
fff    0    0    666    
ggg    0    0    777