use strict;
use warnings;
use Data::Dumper;
##########################################
my (%hist1, %hist2, %hist3);
my  @required_keys;

while (<DATA>) {
  chomp;
  my @element = split;
  my $col0= shift @element; 
  if ($col0 == 1){
    $hist1{$_}++ for @element;
  } elsif ($col0 == 0){
    $hist2{$_}++ for @element;
  } elsif ($col0 == 5){
    $hist3{$_}++ for @element;
  } else {
    #do stuff here when all else fails, undef/NaNs
    print "WTF \n";
  }
};

print Dumper \%hist1;
# using your __DATA__ section, not repeated here for brevity