sub getsubset {
	my ($data,$range) = @_;
	my $cols = @{$$data[0]};
	@$_==$cols or croak "data not rectangular" for @$data;
	$range = rangeparse($range) unless ref $range eq 'ARRAY';
	@$range==4 or croak "bad size of range";
	my @max = (0+@$data,$cols)x2;
	for my $i (0..3) {
		$$range[$i]=$max[$i] if $$range[$i]<0;
		croak "index $i out of range"
			if $$range[$i]<1 || $$range[$i]>$max[$i];
	}
	croak "bad rows $$range[0]-$$range[2]" if $$range[0]>$$range[2];
	croak "bad cols $$range[1]-$$range[3]" if $$range[1]>$$range[3];
	my @cis = $$range[1]-1 .. $$range[3]-1;
	return [ map { sub{\@_}->(@{$$data[$_]}[@cis]) }
		$$range[0]-1 .. $$range[2]-1 ]
}