[Solved] How to compare and merge multiple files?

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I think something like this should do what you want. We use a hash to gather the ‘reference’ file and turn it into a set of keys with an empty array.

Then we iterate on the other files, extracting ‘3 values’ as key, and the last value as an actual value.

And then we compare the two, updating the ‘reference’ hash with either the value or zero. The caveat here – any lines not in your reference file (or duplicates) will just disappear. 

#!/usr/bin/perl

use strict;
use warnings;
use autodie;


#read 'reference file' into a hash:
my %ref;
open( my $ref_fh, "<", "reference_file" );
while (<$ref_fh>) {
    my ( $first, $second, $third ) = split;

    #turn the first three fields into space delimited key.
    $ref{"$first $second $third"} = ();
}

#open each of the files.
my @files = qw ( file1 file2 file3 file4 file5 file6 );
foreach my $input (@files) {
    open( my $input_fh, "<", $input );
    my %current;
    while (<$input_fh>) {

        #line by line, extract 'first 3 fields' to use as a key.
        #then 'value' which we store.
        my ( $first, $second, $third, $value ) = split;
        $current{"$first $second $third"} = $value;
    }

    #refer to 'reference file' and insert matching value or zero into
    #the array.
    foreach my $key ( keys %ref ) {
        push( @{ $ref{$key} }, $current{$key} ? $current{$key} : 0 );
    }
}

foreach my $key ( keys %ref ) {
    print join( " ", $key, @{ $ref{$key} } );
}

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solved How to compare and merge multiple files?