use multiple values as a key in a Perl hash

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";
 }
 }

serenesat · Accepted Answer · 2015-08-25 12:12:38Z

3

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";
     }
 }

edited Aug 25, 2015 at 12:12

serenesat

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answered Aug 25, 2015 at 9:15

Orabîg

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Comments

Jens · Accepted Answer · 2015-08-25 09:15:35Z

1

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};

answered Aug 25, 2015 at 9:15

Jens

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