use strict;

# returns the data as an array ref
my $data = get_graph_data('header_data.dat', 'daily_data*.dat');

sub get_graph_data {
    my ($header,$file_name_format) = @_;

    my @dailies = glob($file_name_format);
    my @data;

    @dailies =
        map  { $_->[0] }
        sort { $a->[1] <=> $b->[1] }
        map  { [ $_, get_number_in_string($_) ] }
            @dailies;
            
    foreach my $file ( $header, @dailies ) {
        local *IN;
        open  IN, "< $file" or die "Cannot open ($file) for reading: $!";
        push @data => [<IN>];
        close IN            or die "Cannot close ($file): $!";
    }
    return \@data;
}

sub get_number_in_string {
    # returns the first instance of one or more digits in string
    my $string = shift || '';
    my ($number) = $string =~ /^([[:digit:]]+)$/;
    return $number;
}