Reimplement reducedim_init for extrema

Update reducedim.jl

Update reducedim.jl

Author: N5N3

base/reducedim.jl

@@ -151,6 +151,23 @@ function reducedim_init(f::F, op::Union{typeof(min),typeof(max)}, A::AbstractArr
     return map!(f, reducedim_initarray(A,region,_InitialValue(),Tr), A1)
 end
 
+function reducedim_init(f::ExtremaMap, op::typeof(_extrema_rf), A::AbstractArray, region)
+    ri = reduced_indices(A, region)
+    any(i -> isempty(axes(A, i)), region) && _empty_reduce_error()
+    A1 = view(A, ri...)
+    T = _return_type(f.f, Tuple{eltype(A)})
+    if isempty(A) || (isconcretetype(nonmissingtype(T)) &&
+                      T === _return_type(min, Tuple{T,T}) &&
+                      T === _return_type(max, Tuple{T,T}) )
+        Tr = T isa Union ? Union{NTuple{2,T.a},NTuple{2,T.b}} : NTuple{2,T}
+        return map!(f, reducedim_initarray(A,region,_InitialValue(),Tr), A1)
+    end
+    v0 = mapreduce(f, op, A1)                          # Try to reduce A1
+    T = _realtype(f.f, promote_union(eltype(A)))       # A possible wrong guess.
+    Tr = v0 isa NTuple{2,T} ? NTuple{2,T} : typeof(v0) # If NTuple{2,T} is wrong. Use typeof(v0) instead.
+    return map!(f, reducedim_initarray(A,region,_InitialValue(),Tr), A1)
+end
+
 reducedim_init(f::Union{typeof(abs),typeof(abs2)}, op::typeof(max), A::AbstractArray{T}, region) where {T} =
     reducedim_initarray(A, region, zero(f(zero(T))), _realtype(f, T))