Faster conversion to dense matrix (#328)

Co-authored-by: Fredrik Ekre <[email protected]>

Author: KnutAM

src/sparsematrix.jl

@@ -641,6 +641,32 @@ function copyto!(dest::AbstractMatrix, Rdest::CartesianIndices{2},
     return dest
 end
 
+# Faster version for non-abstract Array and SparseMatrixCSC 
+function Base.copyto!(A::Array{T}, S::SparseMatrixCSC{<:Number}) where {T<:Number}
+    isempty(S) && return A
+    length(A) < length(S) && throw(BoundsError())
+    
+    # Zero elements that are also in S, don't change rest of A 
+    @inbounds for i in 1:length(S)
+        A[i] = zero(T)
+    end
+    # Copy the structural nonzeros from S to A using 
+    # the linear indices (to work when size(A)!=size(S))
+    num_rows = size(S,1)
+    rowval = getrowval(S)
+    nzval = getnzval(S)
+    linear_index_col0 = 0   # Linear index before column (linear index = linear_index_col0 + row)
+    for col in 1:size(S, 2)
+        for i in nzrange(S, col)
+            row = rowval[i]
+            val = nzval[i]
+            A[linear_index_col0+row] = val
+        end
+        linear_index_col0 += num_rows
+    end
+    return A
+end
+
 ## similar
 #
 # parent method for similar that preserves stored-entry structure (for when new and old dims match)
@@ -922,7 +948,7 @@ function sparse_with_lmul(Tv, Ti, Q)
     return SparseMatrixCSC{Tv,Ti}(size(Q)..., colptr, rowval, nzval)
 end
 
-# converting from SparseMatrixCSC to other matrix types
+# converting from AbstractSparseMatrixCSC to other matrix types
 function Matrix(S::AbstractSparseMatrixCSC{Tv}) where Tv
     _checkbuffers(S)
     A = Matrix{Tv}(undef, size(S, 1), size(S, 2))

test/sparsematrix_constructors_indexing.jl

@@ -36,6 +36,7 @@ end
     @test SparseMatrixCSC{eltype(a), Int}(a) == a
     @test SparseMatrixCSC{eltype(a)}(Array(a)) == a
     @test Array(SparseMatrixCSC{eltype(a), Int8}(a)) == Array(a)
+    @test collect(a) == a
 end
 
 @testset "sparse matrix construction" begin
@@ -301,7 +302,8 @@ end
 @testset "copyto!" begin
     A = sprand(5, 5, 0.2)
     B = sprand(5, 5, 0.2)
-    copyto!(A, B)
+    Ar = copyto!(A, B)
+    @test Ar === A
     @test A == B
     @test pointer(nonzeros(A)) != pointer(nonzeros(B))
     @test pointer(rowvals(A)) != pointer(rowvals(B))
@@ -339,7 +341,9 @@ end
     B = sprand(5, 5, 1.0)
     A = rand(5,5)
     A´ = similar(A)
-    @test copyto!(A, B) == copyto!(A´, Matrix(B))
+    Ac = copyto!(A, B)
+    @test Ac === A 
+    @test A == copyto!(A´, Matrix(B))
     # Test copyto!(dense, Rdest, sparse, Rsrc)
     A = rand(5,5)
     A´ = similar(A)
@@ -354,11 +358,15 @@ end
     @test Matrix(B´)[Rdest] == Matrix(B)[Rsrc]
     # Test that only elements at overlapping linear indices are overwritten
     A = sprand(3, 3, 1.0); B = ones(4, 4)
-    copyto!(B, A)
+    Bc = copyto!(B, A)
     @test B[4, :] != B[:, 4] == ones(4)
+    @test Bc === B
     # Allow no-op copyto! with empty source even for incompatible eltypes
     A = sparse(fill("", 0, 0))
     @test copyto!(B, A) == B
+
+    # Test correct error for too small destination array
+    @test_throws BoundsError copyto!(rand(2,2), sprand(3,3,0.2))
 end
 
 @testset "getindex" begin

test/sparsevector.jl

@@ -59,6 +59,7 @@ end
         @test isa(Array(x), Vector{Float64})
         @test Array(x) == xf
         @test Vector(x) == xf
+        @test collect(x) == xf
     end
 end
 @testset "show" begin