#!/usr/bin/perl 
use warnings;
use strict;

use Data::Dumper;

my $filepath = "OP.txt";
my $olddata = readdt2($filepath);
print Dumper($olddata);
sub readdt2 {
  
  my $ifn = shift;
  open(my $IFH, "<$ifn") or die "cannot open file $ifn\n";
  my $line;
  my @nt = ("A","C","G","T");
  my %ret;
  my @tmp;
  for my $j(@nt) {
    $ret{$j} = [];
    $line = <$IFH>;
    chomp($line);
    @tmp = split(/\s+/,$line);
       for (my $i=0; $i<=$#tmp; $i++ ) {
         $ret{$j}[$i]= $tmp[$i] ;
       }
  }
  close($IFH);
  return(\%ret);
}