Linear indexing with Block broken?

[tkf]

For a matrix M, we have M[1, 1] == M[1]. However, similar indexing with Block seems to be broken:

julia> A = PseudoBlockArray(rand(2,3), [1,1], [2,1])
2×2-blocked 2×3 PseudoBlockArray{Float64,2}:
 0.969606  0.569278  │  0.767362
 ────────────────────┼──────────
 0.331377  0.40404   │  0.549861

julia> A[Block(1)]
1-element Array{Float64,1}:
 0.9696062405354238

julia> A[Block(1), Block(1)]
1×2 view(::Array{Float64,2}, 1:1, 1:2) with eltype Float64:
 0.969606  0.569278

I expect A[Block(1)] and A[Block(1), Block(1)] above to return equivalent matrices. (Or throwing with A[Block(1)] might be OK.)

---

This is also true with BlockArray:

julia> bs = permutedims(reshape([
                  1ones(1, 3), 2ones(1, 2),
                  3ones(2, 3), 4ones(2, 2),
              ], (2, 2)))
2×2 Array{Array{Float64,2},2}:
 [1.0 1.0 1.0]               [2.0 2.0]
 [3.0 3.0 3.0; 3.0 3.0 3.0]  [4.0 4.0; 4.0 4.0]

julia> a = mortar(bs)
2×2-blocked 3×5 BlockArray{Float64,2}:
 1.0  1.0  1.0  │  2.0  2.0
 ───────────────┼──────────
 3.0  3.0  3.0  │  4.0  4.0
 3.0  3.0  3.0  │  4.0  4.0

julia> a[Block(1), Block(1)]
1×3 Array{Float64,2}:
 1.0  1.0  1.0

julia> a[Block(1)]
1-element Array{Float64,1}:
 1.0

[dlfivefifty]

Yes this is not intentional, didn't think about this case when designing the code, and surprised it doesn't error out.

The way I would fix this is to first get it working on views and then use ArrayLayouts.jl approach of materializing a view (adding getindex(a::AbstractArray, K::Block{1}) = layout_getindex(a, K) will materialize a view).

What goes wrong with views is that it tries to reshape to a vector:

julia> view(a,Block(1))
1-element view(reshape(::PseudoBlockArray{Float64,2,Array{Float64,2},Tuple{BlockedUnitRange{Array{Int64,1}},BlockedUnitRange{Array{Int64,1}}}}, 15), BlockSlice(Block(1),1:1)) with eltype Float64:
 1.0

Probably an overload of _maybe_reshape_parent will help, though we'll need to add support for block ReshapedArrays.

[dlfivefifty]

Fixed by #156