Fix reductions over dimensions (#108)

Fixes #92
Fixes #107

Author: timholy

src/axes.jl

@@ -132,6 +132,9 @@ offset_coerce(::Type{I}, r::AbstractUnitRange) where I<:AbstractUnitRange{T} whe
 # issue 100: IdOffsetRange as another index-preserving case shouldn't comtribute offsets
 @inline Base.compute_offset1(parent, stride1::Integer, dims::Tuple{Int}, inds::Tuple{IdOffsetRange}, I::Tuple) =
     Base.compute_linindex(parent, I) - stride1*first(axes(parent, dims[1]))
+Base.reduced_index(i::IdOffsetRange) = typeof(i)(first(i):first(i))
+# Workaround for #92 on Julia < 1.4
+Base.reduced_index(i::IdentityUnitRange{<:IdOffsetRange}) = typeof(i)(first(i):first(i))
 
 @inline function Base.iterate(r::IdOffsetRange)
     ret = iterate(r.parent)

test/runtests.jl

@@ -542,6 +542,11 @@ end
     @test maximum(A) == maximum(parent(A))
     @test minimum(A) == minimum(parent(A))
     @test extrema(A) == extrema(parent(A))
+    @test sum(A) == sum(parent(A))
+    @test sum(A, dims=1) == OffsetArray(sum(parent(A), dims=1), A.offsets)
+    @test sum(A, dims=2) == OffsetArray(sum(parent(A), dims=2), A.offsets)
+    @test sum(A, dims=(1,2)) == OffsetArray(sum(parent(A), dims=(1,2)), A.offsets)
+    @test sum(view(OffsetArray(reshape(1:27, 3, 3, 3), 0, 0, 0), :, :, 1:2), dims=(2,3)) == reshape([51,57,63], 3, 1, 1)
     C = similar(A)
     cumsum!(C, A, dims = 1)
     @test parent(C) == cumsum(parent(A), dims = 1)