Perl merging columns in two text files - perl

Question

I am a beginner with Perl and I want to merge the content of two text files.
I have read some similar questions and answers on this forum, but I still cannot resolve my issues
The first file has the original ID and the recoded ID of each individual (in the first and fourth columns)
The second file has the recoded ID and some information on some of the individuals (in the first and second columns).
I want to create an output file with the original, recoded and information of these individuals.
This is the perl script I have created so far, which is not working.
If anyone could help it would be very much appreciated.
use warnings;
use strict;
use diagnostics;
use vars qw( #fields1 $recoded $original $IDF #fields2);
my %columns1;
open (FILE1, "<file1.txt") || die "$!\n Couldn't open file1.txt\n";
while ($_ = <FILE1>)
{
chomp;
#fields1=split /\s+/, $_;
my $recoded = $fields1[0];
my $original = $fields1[3];
my %columns1 = (
$recoded => $original
);
};
open (FILE2, "<file2.txt") || die "$!\n Couldnt open file2.txt \n";
for ($_ = <FILE2>)
{
chomp;
#fields2=split /\s+/, $_;
my $IDF= $fields2[0];
my $F=$fields2[1];
my %columns2 = (
$F => $IDF
);
};
close FILE1;
close FILE2;
open (FILE3, ">output.txt") ||die "output problem\n";
for (keys %columns1) {
if (exists ($columns2{$_}){
print FILE3 "$_ $columns1{$_}\n"
};
}
close FILE3;

Answer 1

One problem is with scoping. In your first loop, you have a my in front of $column1 which makes it local to the loop and will not be in scope when you next the loop. So the %columns1 (which is outside of the loop) does not have any values set (which is what I suspect you want to set). For the assignment, it would seem to be easier to have $columns1{$recorded} = $original; which assigns the value to the key for the hash.
In the second loop you need to declare %columns2 outside of the loop and possibly use the above assignment.
For the third loop, in the print you just need add $columns2{$_} in front part of the string to be printed to get the original ID to be printed before the recorded ID.

Answer 2

Scope:
The problem is with scope of the hash variables you have defined. The scope of the variable is limited to the loop inside which the variable has been defined.
In your code, since %columns1 and %columns2 are used outside the while loops. Hence, they should be defined outside the loops.
Compilation error : braces not closed properly
Also, in the "if exists" part, the open-and-closed braces symmetry is affected.
Here is your code with the required corrections made:
use warnings;
use strict;
use diagnostics;
use vars qw( #fields1 $recoded $original $IDF #fields2);
my (%columns1, %columns2);
open (FILE1, "<file1.txt") || die "$!\n Couldn't open CFC_recoded.txt\n";
while ($_ = <FILE1>)
{
chomp;
#fields1=split /\s+/, $_;
my $recoded = $fields1[0];
my $original = $fields1[3];
%columns1 = (
$recoded => $original
);
}
open (FILE2, "<file2.txt") || die "$!\n Couldnt open CFC_F.xlsx \n";
for ($_ = <FILE2>)
{
chomp;
#fields2=split /\s+/, $_;
my $IDF= $fields2[0];
my $F=$fields2[1];
%columns2 = (
$F => $IDF
);
}
close FILE1;
close FILE2;
open (FILE3, ">output.txt") ||die "output problem\n";
for (keys %columns1) {
print FILE3 "$_ $columns1{$_} \n" if exists $columns2{$_};
}
close FILE3;