Rotation functions for sparse matrices

[kshyatt]

Although rot180(A::AbstractArray, k::Int), rotr90(A::AbstractArray, k::Int), and rotl90(A::AbstractArray, k::Int) are supposed to accept AbstractArrays, if you actually tried to use them with sparse matrices they'd fail because the matrix-argument-only versions only supported StridedMatrix objects. I added rotations for SparseMatrixCSC matrices as well as some tests.

[timholy]

Couldn't this still be called I? (It would avoid an allocation.)

[kshyatt]

I will test it out (probably, yes, and then I can do the same in rotl90). It works! Pushed and hopefully ci completes soon.

[timholy]

When writing new tests discovers missing methods, and then those methods get implemented, Progress Is Being Made 😄.

[tkelman]

Indeed. I believe @kshyatt was also intending to add some docs for the not-yet-documented rotation methods that take an integer second argument. Also it would be interesting to compare the performance of this to a method that uses the colptr and rowval fields of the CSC format directly, as opposed to converting to-then-from coordinate format with findnz and sparse. That's a performance optimization and can be pursued as a future enhancement though.

[timholy]

This passed on travis; since the earlier incarnation also passed AV, I'm merging.

[ViralBShah]

👍

[ViralBShah]

If we have something like mapnz, we can do it for all the math operations without replicating the code again for sparse matrices (#7010). Right now, they are all going to be really slow.

[tkelman]

I'm not sure whether map is exactly the interface you want here. Something more like enumerate, probably.

[ViralBShah]

Backported to 0.3 in 8d6a61b