From: grzegorz.jakubiak@... Date: 2020-10-22T06:02:39+00:00 Subject: [ruby-core:100493] [Ruby master Feature#17277] Make Enumerator#with_index yield row and col indices for Matrix Issue #17277 has been updated by greggzst (Grzegorz Jakubiak). greggzst (Grzegorz Jakubiak) wrote in #note-2: > I also noticed when combining `each_with_index` with `inject` it passes `element, row_index and col_index` as one argument to the block > > ```ruby > Matrix[[1,2,4,5],[7,8,9,2]].each_with_index.inject({}) { |acc, e, row, col| puts "#{acc}, #{e}, #{row}, #{col}"; acc[[e[1],e[2]]] = e[0]; acc } > {}, [1, 0, 0], , > {[0, 0]=>1}, [2, 0, 1], , > {[0, 0]=>1, [0, 1]=>2}, [4, 0, 2], , > {[0, 0]=>1, [0, 1]=>2, [0, 2]=>4}, [5, 0, 3], , > {[0, 0]=>1, [0, 1]=>2, [0, 2]=>4, [0, 3]=>5}, [7, 1, 0], , > {[0, 0]=>1, [0, 1]=>2, [0, 2]=>4, [0, 3]=>5, [1, 0]=>7}, [8, 1, 1], , > {[0, 0]=>1, [0, 1]=>2, [0, 2]=>4, [0, 3]=>5, [1, 0]=>7, [1, 1]=>8}, [9, 1, 2], , > {[0, 0]=>1, [0, 1]=>2, [0, 2]=>4, [0, 3]=>5, [1, 0]=>7, [1, 1]=>8, [1, 2]=>9}, [2, 1, 3], , > => {[0, 0]=>1, [0, 1]=>2, [0, 2]=>4, [0, 3]=>5, [1, 0]=>7, [1, 1]=>8, [1, 2]=>9, [1, 3]=>2} > ``` > My bad I just figured out that's a case for `inject` so it shouldn't be considered in this discussion. Anyways it'd be good to have `with_index` chained to whatever enumerator returning Matrix indices ---------------------------------------- Feature #17277: Make Enumerator#with_index yield row and col indices for Matrix https://bugs.ruby-lang.org/issues/17277#change-88112 * Author: greggzst (Grzegorz Jakubiak) * Status: Assigned * Priority: Normal * Assignee: marcandre (Marc-Andre Lafortune) ---------------------------------------- Currently this code seems to be counting index based on the internal array of arrays and it's not correct for the matrix which should return row and col indices ``` Matrix[[0,2,3,4], [6,7,8,9], [1,4,5,8]].each.with_index { |e, index| print "#{index} " } ; puts 0 1 2 3 4 5 6 7 8 9 10 11 => nil ``` I'm aware of the fact that you could do following and you get the correct results: ``` Matrix[[0,2,3,4], [6,7,8,9], [1,4,5,8]].each_with_index { |e, row, col| print "[#{row}, #{col}] " } ; puts [0, 0] [0, 1] [0, 2] [0, 3] [1, 0] [1, 1] [1, 2] [1, 3] [2, 0] [2, 1] [2, 2] [2, 3] => nil ``` You can even chain `each_with_index` with other enumerators and access indices within them e.g. ``` Matrix[[0,2,3,4], [6,7,8,9], [1,4,5,8]].each_with_index.filter_map { |e, row, col| [row, col] if e % 4 == 0} => [[0, 0], [0, 3], [1, 2], [2, 1], [2, 3]] ``` However, I feel we should override `with_index` for Matrix so it returns row and col indices. -- https://bugs.ruby-lang.org/ Unsubscribe: