SubArrays and reduce/map

[tshort]

I don't see a way to run reduce operations on SubArrays of NullableArrays.

julia> a = NullableArray([1:5;])

julia> nullify!(a,1)

julia> reduce(+, a, skipnull=true)
Nullable(14)

julia> reduce(+, sub(a, 1:4), skipnull=true)
ERROR: MethodError: `reduce` has no method matching reduce(::Function, ::SubArray{Nullable{Int64},1,NullableArrays.NullableArray{Int64,1},Tuple{UnitRange{Int64}},1})
Closest candidates are:
  reduce(::Any, ::Any)
  reduce(::Any, ::Any, ::Any)
  reduce(::Any, ::Number)
  ...

It would be nice to have a more generic way to indicate how to treat nulls during reduction, for example:

reduce(+, skipnulls(a))
reduce(+, skipnulls(sub(a, 1:4)))
sum(skipnulls(a))
sum(skipnulls(sub(a, 1:4)))

Here, skipnulls could return a simple iterator or a wrapper type.

Also, map with the lift= argument doesn't support SubArrays of NullableArrays.

[davidagold]

That's a very interesting proposal (the skipnulls constructor).

I have exams for my first quarter of graduate school through this coming Tuesday. After that I'll have time at least to implement a reduce methods for SubArrays of NullableArrays, and hopefully also to experiment with the API you suggest.