Define reducedim_initarray(A, region, ::UndefInitializer, ::Type) for easier initialization

Author: N5N3

base/reducedim.jl

@@ -91,7 +91,8 @@ end
 # reducedim_initarray is called by
 reducedim_initarray(A::AbstractArrayOrBroadcasted, region, init, ::Type{R}) where {R} = fill!(similar(A,R,reduced_indices(A,region)), init)
 reducedim_initarray(A::AbstractArrayOrBroadcasted, region, init::T) where {T} = reducedim_initarray(A, region, init, T)
-
+# TODO: extend this to minimum and maximum
+reducedim_initarray(A::AbstractArrayOrBroadcasted, region, ::UndefInitializer, ::Type{R}) where {R} = similar(A,R,reduced_indices(A,region))
 # TODO: better way to handle reducedim initialization
 #
 # The current scheme is basically following Steven G. Johnson's original implementation

stdlib/LinearAlgebra/src/special.jl

@@ -7,7 +7,8 @@
 # Diagonal/Bidiagonal/Tridiagonal/SymTridiagonal matrix. However, reducedim should
 # yield a dense vector to increase performance.
 Base.reducedim_initarray(A::Union{Diagonal,Bidiagonal,Tridiagonal,SymTridiagonal}, region, init, ::Type{R}) where {R} = fill(convert(R, init), Base.reduced_indices(A,region))
-
+Base.reducedim_initarray(A::Union{Diagonal,Bidiagonal,Tridiagonal,SymTridiagonal}, region, ::UndefInitializer, ::Type{R}) where {R} =
+    Array{R}(undef, Base.to_shape(Base.reduced_indices(A, region)))
 
 # Interconversion between special matrix types
 

stdlib/SparseArrays/src/sparsematrix.jl

@@ -1879,6 +1879,8 @@ end
 function Base.reducedim_initarray(A::AbstractSparseMatrixCSC, region, v0, ::Type{R}) where {R}
     fill!(Array{R}(undef, Base.to_shape(Base.reduced_indices(A, region))), v0)
 end
+Base.reducedim_initarray(A::AbstractSparseMatrixCSC, region, ::UndefInitializer, ::Type{R}) where {R} =
+    Array{R}(undef, Base.to_shape(Base.reduced_indices(A, region)))
 
 # General mapreduce
 function _mapreducezeros(f, op, ::Type{T}, nzeros::Integer, v0) where T

stdlib/SparseArrays/src/sparsevector.jl

@@ -2145,3 +2145,6 @@ function circshift!(O::SparseVector, X::SparseVector, (r,)::Base.DimsInteger{1})
 end
 
 circshift!(O::SparseVector, X::SparseVector, r::Real,) = circshift!(O, X, (Integer(r),))
+
+Base.reducedim_initarray(A::SparseVector, region, ::UndefInitializer, ::Type{R}) where {R} =
+    Array{R}(undef, Base.to_shape(Base.reduced_indices(A, region)))