getindex

Project.toml

@@ -4,6 +4,7 @@ authors = ["Jorge Fernandez-de-Cossio-Diaz <j.cossio.diaz@gmail.com>"]
 version = "0.1.0"
 
 [deps]
+LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 StructArrays = "09ab397b-f2b6-538f-b94a-2f83cf4a842a"
 Zygote = "e88e6eb3-aa80-5325-afca-941959d7151f"
 

src/ZygoteStructArrays.jl

@@ -1,7 +1,7 @@
 module ZygoteStructArrays
 
-using Zygote, StructArrays
-using Zygote: @adjoint, literal_getproperty
+using Zygote, StructArrays, LinearAlgebra
+using Zygote: @adjoint, Numeric, literal_getproperty, accum
 
 include("adjoints.jl")
 

src/adjoints.jl

@@ -10,7 +10,7 @@ end
 
 @adjoint function (::Type{T})(t::NamedTuple) where {T<:StructArray}
     result = T(t)
-    back(Δ::NamedTuple) = (fieldarrays(T(Δ)),)
+    back(Δ::NamedTuple) = (NamedTuple{propertynames(result)}(Δ),)
     function back(Δ::AbstractArray{<:NamedTuple})
         nt = (; (p => [dx[p] for dx in Δ] for p in propertynames(result))...)
         return back(nt)
@@ -22,7 +22,7 @@ end
     key::Symbol
     result = getproperty(sa, key)
     function back(Δ::AbstractArray)
-        nt = (; (p => zero(getproperty(sa, p)) for p in propertynames(sa))...)
+        nt = (; (k => zero(v) for (k,v) in pairs(fieldarrays(sa)))...)
         return (Base.setindex(nt, Δ, key), nothing)
     end
     return result, back
@@ -33,3 +33,25 @@ end
     back(Δ::NamedTuple) = (values(T(Δ)),)
     return result, back
 end
+
+@adjoint Base.getindex(x::StructArray, i...) = x[i...], Δ -> ∇getindex(x, i, Δ)
+@adjoint Base.view(x::StructArray, i...) = view(x, i...), Δ -> ∇getindex(x, i, Δ)
+function ∇getindex(x::StructArray, i, Δ::NamedTuple)
+    dx = (; (k => ∇getindex(v, i, Δ[k]) for (k,v) in pairs(fieldarrays(x)))...)
+    di = map(_ -> nothing, i)
+    return (dx, map(_ -> nothing, i)...)
+end
+# based on 
+# https://github.com/FluxML/Zygote.jl/blob/64c02dccc698292c548c334a15ce2100a11403e2/src/lib/array.jl#L41
+∇getindex(x::AbstractArray, i, Δ::Nothing) = nothing
+function ∇getindex(x::AbstractArray, i, Δ)
+    if i isa NTuple{<:Any, Integer}
+        dx = Zygote._zero(x, typeof(Δ))
+        dx[i...] = Δ
+    else
+        dx = Zygote._zero(x, eltype(Δ))
+        dxv = view(dx, i...)
+        dxv .= Zygote.accum.(dxv, Zygote._droplike(Δ, dxv))
+    end
+    return dx
+end

test/adjoints.jl

@@ -29,3 +29,18 @@ end == ([1.0, 1.0], [2.0, 2.0])
     S = StructArray{Complex}((im = Y, re = X))
     sum(S).re + 2sum(S).im
 end == ([1.0, 1.0], [2.0, 2.0])
+
+@test gradient(randn(2), randn(2)) do X, Y
+    S = StructArray{Complex}((re = X, im = Y))
+    S[1].re
+end == ([1.0, 0.0], nothing)
+
+@test gradient(randn(2), randn(2)) do X, Y
+    S = StructArray{Complex}((re = X, im = Y))
+    S[1].re + S[1].im
+end == ([1.0, 0.0], [1.0, 0.0])
+
+@test gradient(randn(2), randn(2)) do X, Y
+    S = StructArray{Complex}((re = X, im = Y))
+    S[1].re + S[2].re
+end == ([1.0, 1.0], nothing)