use multiple values as a key in a Perl hash - perl

Question

I have two tables. First one is $sampleand looks like this:
col1 col2
A 1
A 3
A 4
B 7
... ...
Second one is $exonand looks like this:
col1 col2 col3 col4 col5
name1 A 1 100 200
name2 A 2 300 400
name3 A 3 500 600
name4 A 4 700 800
I want to check if there is a match between col1 and col2 from $sampleand col2 and col3from exon.
I normally use hashes for this in Perl. I know how it works when you are just looking for a match between two columns. But I'm stuck now because values from two columns should match. This is what I have for now
my %hash = ();
while(<$sample>){
chomp;
my #cols = split(/\t/);
my $keyfield = $cols[0]; #col1
my $keyfield2 = $cols[1]; #col2
push #{ $hash{$keyfield}}, $keyfield2}; #this is probably not correct
}
seek $exon,0,0; #cursor resetting
while(<$exon>){
chomp;
my #cols = split(/\t/);
my $keyfield = $cols[1]; #col2
my $keyfield2 = $cols[2]; #col3
if (exists($hash{$keyfield}) && exists($hash{$keyfield2})) {
print $output $cols[0], "\t", $cols[3], "\t", $cols[4], "\n";
}
}

Answer 1

You should use a concatenation of col2 and col3 values as the keys for your hastable
my %hash = ();
while(<$sample>){
chomp;
my #cols = split(/\t/);
my $keyfield = $cols[0] #col1
my $keyfield2 = $cols[1] #col2
my $key = "$keyfield - $keyfield2";
$hash{$key}=1;
}
seek $exon,0,0 #cursor resetting
while(<$exon>){
chomp;
my #cols = split(/\t/);
my $keyfield = $cols[1]; #col2
my $keyfield2 = $cols[2]; #col3
my $key = "$keyfield - $keyfield2";
if (exists($hash{$key}) {
print $output $cols[0], "\t", $cols[3], "\t", $cols[4], "\n";
}
}

Answer 2

You can put both fields as key separarted with a delimiter in your hash:
my #cols = split(/\t);
my $keyfield = $cols[0]."--".$cols[1];
push #{ $hash{$keyfield}}, value};