csv2json: Check for duplicate entries

@stations = sort { $a->{name} cmp $b->{name} } @stations;

my $have_duplicates = 0;

my @names           = map { $_->{name} } @stations;

my @ds100           = map { $_->{ds100} } @stations;

my @uic_ids         = map { $_->{uic} } @stations;

for my $i ( 1 .. $#names ) {

	if ( $names[ $i - 1 ] eq $names[$i] ) {

		say "Duplicate station name: $names[$i]";

		$have_duplicates = 1;

	}

}

for my $i ( 1 .. $#ds100 ) {

	if ( $ds100[ $i - 1 ] eq $ds100[$i] ) {

		say "Duplicate DS100 code: $ds100[$i]";

		$have_duplicates = 1;

	}

}

for my $i ( 1 .. $#uic_ids ) {

	if ( $uic_ids[ $i - 1 ] == $uic_ids[$i] ) {

		say "Duplicate UIC ID: $uic_ids[$i]";

		$have_duplicates = 1;

	}

}

if ($have_duplicates) {

	say "Data has NOT been converted to stations.json";

	say "Please remove duplicates and run $0 again";

}

my $json_out = JSON->new->utf8->canonical->pretty->encode( [@stations] );

write_file( 'stations.json', $json_out );