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

Author: abraunst

stdlib/SparseArrays/src/sparsematrix.jl

@@ -328,8 +328,12 @@ function _sparsesimilar(S::SparseMatrixCSC, ::Type{TvNew}, ::Type{TiNew}) where
     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))
+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))