G'day sidsinha,

"I have a string which contains data that can be split with "/\s+/" however, the data with which I want to plot the graph lies in column 3 and column 4."

Just ignore the values you don't want by assigning them to undef. Here's the technique (I'm assuming there's no Column 0):

$ perl -Mstrict -Mwarnings -le '
    my $x = "a b c d";
    my (undef, undef, $c, $d) = split /\s+/ => $x;
    print "$c $d";
'
c d
[download]

Update: That looks a tad clunky. Instead, you can take a slice of the split results: this might be better if you have more than four columns.

$ perl -Mstrict -Mwarnings -le '
    my $x = "a b c d";
    my ($c, $d) = (split /\s+/ => $x)[2,3];
    print "$c $d";
'
c d
[download]