bugfix: Respect init value in reduction (#366)

Author: dkarrasch

src/sparsematrix.jl

@@ -2373,7 +2373,7 @@ function Base._mapreducedim!(f, op, R::AbstractArray, A::AbstractSparseMatrixCSC
 
     if size(R, 1) == size(R, 2) == 1
         # Reduction along both columns and rows
-        R[1, 1] = mapreduce(f, op, A)
+        R[1, 1] = op(R[1, 1], mapreduce(f, op, A))
     elseif size(R, 1) == 1
         # Reduction along rows
         _mapreducerows!(f, op, R, A)

test/sparsematrix_ops.jl

@@ -190,6 +190,10 @@ dA = Array(sA)
         end
     end
 
+    for s0 in (spzeros(3, 7), spzeros(1, 3), spzeros(3, 1)), d in (1, 2, 3, (1,2))
+        @test all(isone, sum(s0, dims=d, init=1.0))
+    end
+
     for f in (sum, prod, minimum, maximum)
         # Test with a map function that maps to non-zero
         for arr in (se33, sA, pA)