logistic

#!/usr/bin/perl -w
#
# Replace vw linear regressor prediction by the logistic link
# Prediction/label is assumed to be the first item on each line
# Rest of line (if present) remains intact
#
use Getopt::Std;
use vars qw($opt_0 $opt_1);

#
# traditional logistic function: [0..1] range
#
sub logistic_01($) {
    1.0 / (1.0 + exp(-$_[0]));
}

#
# logistic function mapped to [-1 .. 1] range
#
sub logistic_11($) {
    2.0 / (1.0 + exp(-$_[0])) - 1.0;
}

my $LinkFunc = \&logistic_11;

sub usage {
    die "Usage: $0 [Options] [files...]
    Maps label x (1st number on line) to logistic(x)
    Options:
        -0      Use logistic(x) -> [0  .. 1] range
        -1      Use logistic(x) -> [-1 .. 1] range (default)
";
}

sub init {
    $0 =~ s{.*/}{};
    usage() if (@ARGV == 0 && -t STDIN);

    getopts('01');

    if ($opt_0) {
        $LinkFunc = \&logistic_01;
    }
}


#
# -- main
#
init();

while (<>) {
    s/^(\S+)/$LinkFunc->($1)/e;
    print;
}