Range-based indexing #149
Description
Currently, to take a slice of a matrix, one needs to use e.g. the sub_slice function. I propose to add implementations of Index<(Range<usize>, Range<usize>)>. See the following example:
let x = matrix![ 1.0, 2.0, 3.0;
4.0, 5.0, 6.0;
7.0, 8.0, 9.0];
// Want to take the 2x2 lower-right corner
// Current way:
let corner = x.sub_slice([1, 1], 2, 2);
// Range-based indexing:
let corner = x[(1 .. 3, 1 .. 3)];
// Or, more succinctly:
let corner = x[(1 .., 1 ..)];
// More flexible indexing, let's take the two first columns
let two_last_cols = x[( .. 2, ..)]Similarly, we can slice rows or columns (returning Row or Column) using a mix of usize and Range<usize>:
let second_row = x[(1, ..)];
let second_col = x[(.., 1)];
// Only parts of a given row, still returns a `Row` struct
// (so we can extract a raw slice, which is useful for performance)
let parts_of_second_row = x[(1, 1 .. 3 )];The range-based indexing can be implemented in terms of Index<(R1, R2)> where R1, R2 are any of the following concrete types from the stdlib: Range, RangeFull, RangeTo, RangeFrom.
Any thoughts on this? I think it would really empower matrix slices.