Making SparseArrays.jl an external dependency

[MartinuzziFrancesco]

Closes #243

[MartinuzziFrancesco]

Actually I don't this is the correct approach. The sparse solution is returned even without using SparseArrays. However, SparseArrays is not in ReservoirComputing dependencies. I'm getting:

julia> @isdefined ReservoirComputing
true

julia> @isdefined SparseArrays
false

julia> weighted_init(100, 10)
100×10 Matrix{Float32}:
  0.0452399   0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0
 -0.0348047   0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0
 -0.0386004   0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0
  0.00981022  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0
  0.0577838   0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0
 -0.0562827   0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0
  0.0441522   0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0
  0.0788491   0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0
  0.00627948  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0
 -0.0293777   0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0
  ⋮                               ⋮                   
  0.0         0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  -0.041219
  0.0         0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0975579
  0.0         0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  -0.0515611
  0.0         0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  -0.056383
  0.0         0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0956139
  0.0         0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0240148
  0.0         0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.0706484
  0.0         0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  -0.00635637
  0.0         0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0   0.041213

julia> @isdefined SparseArrays
false

julia> weighted_init(100, 10; return_sparse=true)
100×10 SparseArrays.SparseMatrixCSC{Float32, Int64} with 100 stored entries:
⎡⡇⠀⠀⠀⎤
⎢⡇⠀⠀⠀⎥
⎢⢸⠀⠀⠀⎥
⎢⢸⠀⠀⠀⎥
⎢⠀⡇⠀⠀⎥
⎢⠀⡇⠀⠀⎥
⎢⠀⡇⠀⠀⎥
⎢⠀⡇⠀⠀⎥
⎢⠀⢸⠀⠀⎥
⎢⠀⢸⠀⠀⎥
⎢⠀⠀⡇⠀⎥
⎢⠀⠀⡇⠀⎥
⎢⠀⠀⢸⠀⎥
⎢⠀⠀⢸⠀⎥
⎢⠀⠀⢸⠀⎥
⎢⠀⠀⢸⠀⎥
⎢⠀⠀⠀⡇⎥
⎢⠀⠀⠀⡇⎥
⎢⠀⠀⠀⢸⎥
⎣⠀⠀⠀⢸⎦

julia> @isdefined SparseArrays
false

is this expected? or is there a better approach for it? @ChrisRackauckas

[MartinuzziFrancesco]

gente ping on this @ChrisRackauckas

[ChrisRackauckas]

That means there's a dependency that still relies on sparsearrays

[MartinuzziFrancesco]

ah I see, StatsBase.jl seems to be the problem. We only use sample from that library, we should be able to go without it