Make length(A.nzval)==nnz(A) #30662

Author: abraunst

stdlib/SparseArrays/src/sparsematrix.jl

@@ -339,9 +339,13 @@ function _sparsesimilar(S::SparseMatrixCSC, ::Type{TvNew}, ::Type{TiNew}) where
     newrowval = copyto!(similar(S.rowval, TiNew), S.rowval)
     return SparseMatrixCSC(S.m, S.n, newcolptr, newrowval, similar(S.nzval, TvNew))
 end
-# parent methods for similar that preserves only storage space (for when new and old dims differ)
-_sparsesimilar(S::SparseMatrixCSC, ::Type{TvNew}, ::Type{TiNew}, dims::Dims{2}) where {TvNew,TiNew} =
-    SparseMatrixCSC(dims..., fill(one(TiNew), last(dims)+1), similar(S.rowval, TiNew), similar(S.nzval, TvNew))
+# parent methods for similar that preserves only storage space allocation (for when new and old dims differ)
+function _sparsesimilar(S::SparseMatrixCSC, ::Type{TvNew}, ::Type{TiNew}, dims::Dims{2}) where {TvNew,TiNew}
+    S1=spzeros(TvNew, TiNew, dims...)
+    sizehint!(S1.rowval, min(length(S.rowval), length(S1)))
+    sizehint!(S1.nzval, min(length(S.nzval), length(S1)))
+    return S1
+end
 # parent method for similar that allocates an empty sparse vector (when new dims are single)
 _sparsesimilar(S::SparseMatrixCSC, ::Type{TvNew}, ::Type{TiNew}, dims::Dims{1}) where {TvNew,TiNew} =
     SparseVector(dims..., similar(S.rowval, TiNew, 0), similar(S.nzval, TvNew, 0))

stdlib/SparseArrays/test/sparse.jl

@@ -2188,22 +2188,22 @@ end
     @test typeof(simA) == typeof(A)
     @test size(simA) == (6,6)
     @test simA.colptr == fill(1, 6+1)
-    @test length(simA.rowval) == length(A.rowval)
-    @test length(simA.nzval) == length(A.nzval)
+    @test length(simA.rowval) == 0
+    @test length(simA.nzval) == 0
     # test similar with entry type and Dims{2} specification (preserves storage space only)
     simA = similar(A, Float32, (6,6))
     @test typeof(simA) == SparseMatrixCSC{Float32,eltype(A.colptr)}
     @test size(simA) == (6,6)
     @test simA.colptr == fill(1, 6+1)
-    @test length(simA.rowval) == length(A.rowval)
-    @test length(simA.nzval) == length(A.nzval)
+    @test length(simA.rowval) == 0
+    @test length(simA.nzval) == 0
     # test similar with entry type, index type, and Dims{2} specification (preserves storage space only)
     simA = similar(A, Float32, Int8, (6,6))
     @test typeof(simA) == SparseMatrixCSC{Float32, Int8}
     @test size(simA) == (6,6)
     @test simA.colptr == fill(1, 6+1)
-    @test length(simA.rowval) == length(A.rowval)
-    @test length(simA.nzval) == length(A.nzval)
+    @test length(simA.rowval) == 0
+    @test length(simA.nzval) == 0
     # test similar with Dims{1} specification (preserves nothing)
     simA = similar(A, (6,))
     @test typeof(simA) == SparseVector{eltype(A.nzval),eltype(A.colptr)}