topn

#!/usr/bin/perl -wnl

# Reads colum-formatted files and reoutputs the first n unique lines
# Similar to uniq(1) but will take more than just the top n=1 and allows
# specifying which fields to group by, by name

# Usage: topn -n 5 -h tid mndoms 
# For each combination of the columns 'tid' and 'mndoms', prints the first 5 rows
# The -h is to interpret the first row as a header, allows naming columns
# Otherwise, 1-based indexing

# Field numbering begins at 1
# Use negative numbers to start counting from right (-1 downwards). E.g.:
# cat file.csv | field -s , -- -1 -2 1
# This uses comma as a separator, then prints the last, 2nd-to-last, first cols
# The -- is necessary so that the -1 won't be considered a command line option

use strict;
use Getopt::Long;

# Field indices to select and ouptut
our @a;
# Field separator, default (any amount of) whitespace
our $sep;
# If header is enabled
our $header;
# Default number of uniq lines to print
our $n;
BEGIN {
    GetOptions(
        "separator|sep|s=s" => \$sep,
        "header|h" => \$header,
        "lines|n=i" => \$n,
    );
    $sep ||= '\s+';
    $header = 0 unless defined $header;
    $n ||= 1;
    
    # Read all integers from the command line
    while(@ARGV) {
        if ($ARGV[0] =~ /^[\d-]+$/) {
            # Adjusted for 1-based counting
            $ARGV[0] -= 1 if $ARGV[0] > 0;
            push @a, shift;
        } elsif ($ARGV[0] =~ /^[\d]+\.\.[\d]+$/) {
            # Allow ranges like 3..5
            my ($a, $b) = split(/\.\./, shift());
            ($a, $b) = map { $_ - 1 } ($a, $b);
            push @a, ($a .. $b);
        } else {
            print STDERR "Invalid column number: $ARGV[0]\n";
        }
    } 
}


# splits input stream
my @l = split /$sep/o;
# Select all fields if none specified
@a = (0 .. scalar(@l-1)) unless @a;

# Don't consider any columns that doesn't actually exist for this row
my @b = grep { defined($l[$_]) } @a;

our %counts;
my $key = join('', map { $l[$_] } @b);
$counts{$key}++;
if ($counts{$key} > $n) {
    #print STDERR "Skipping";
    next;
}
#print STDERR "Here";
print;