Special case sparse matrix copy! for equal lengths.

If length(A) == length(B) in copy!(A, B), all elements in A are
replaced, even if size(A) != size(B). This can be done much more
efficiently than falling back on copy! for AbstractMatrix, reusing
functionality from reshape instead.

Author: martinholters

base/sparse/sparsematrix.jl

@@ -195,14 +195,19 @@ copy(S::SparseMatrixCSC) =
 
 function copy!{TvA, TiA, TvB, TiB}(A::SparseMatrixCSC{TvA,TiA},
                                    B::SparseMatrixCSC{TvB,TiB})
-    # If the two matrices have the same size then all the
-    # elements in A will be overwritten and we can simply copy the
-    # internal fields of B to A.
-    if size(A) == size(B)
-        copy!(A.colptr, B.colptr)
+    # If the two matrices have the same length then all the
+    # elements in A will be overwritten.
+    if length(A) == length(B)
         resize!(A.nzval, length(B.nzval))
         resize!(A.rowval, length(B.rowval))
-        copy!(A.rowval, B.rowval)
+        if size(A) == size(B)
+            # Simple case: we can simply copy the internal fields of B to A.
+            copy!(A.colptr, B.colptr)
+            copy!(A.rowval, B.rowval)
+        else
+            # This is like a "reshape B into A".
+            sparse_compute_reshaped_colptr_and_rowval(A.colptr, A.rowval, A.m, A.n, B.colptr, B.rowval, B.m, B.n)
+        end
         copy!(A.nzval, B.nzval)
     else
         invoke(Base.copy!, Tuple{AbstractMatrix{TvA}, AbstractMatrix{TvB}}, A, B)

test/sparsedir/sparse.jl

@@ -253,6 +253,10 @@ let
     @test pointer(A.nzval) != pointer(B.nzval)
     @test pointer(A.rowval) != pointer(B.rowval)
     @test pointer(A.colptr) != pointer(B.colptr)
+    # Test size(A) != size(B), but length(A) == length(B)
+    B = sprand(25, 1, 0.2)
+    copy!(A, B)
+    @test A[:] == B[:]
     # Test size(A) != size(B)
     B = sprand(3, 3, 0.2)
     copy!(A, B)