#!/usr/bin/perl

my ($field,%fh);

while ( <DATA> ) {
    @field = split /,/;
    $fh{$field[2]} .= "$field[0],$field[1],$field[3]";
}

for my $file( keys %fh ) {
    open F, ">$file" or die $!;
    print F $fh{$file};
    close F;
}