fixes #582

src/onehot.jl

@@ -78,6 +78,8 @@ onecold(y::AbstractVector, labels = 1:length(y)) = labels[Base.argmax(y)]
 onecold(y::AbstractMatrix, labels...) =
   dropdims(mapslices(y -> onecold(y, labels...), y, dims=1), dims=1)
 
+onecold(y::OneHotMatrix, labels...) = map(x -> onecold(x, labels...), y.data)
+
 function argmax(xs...)
   Base.depwarn("`argmax(...)` is deprecated, use `onecold(...)` instead.", :argmax)
   return onecold(xs...)