Creating tree on views

[BCRARL]

I have a (large) 3 dimensional tensor and want to create a tree using SubArrays

3×3×3 Array{Float64,3}:
[:, :, 1] =
 0.576401   0.152728  0.496296
 0.0284128  0.994683  0.640066
 0.0910659  0.257534  0.939821

[:, :, 2] =
 0.758803   0.0218801  0.192174
 0.591324   0.019357   0.802315
 0.0582035  0.895237   0.474521

[:, :, 3] =
 0.437771   0.333887  0.920422
 0.0445638  0.429712  0.19376 
 0.245626   0.243987  0.065141

But attempting to create a BallTree results in the below error.

julia> NearestNeighbors.BallTree([view(toy,:,2:3,i) for i in 1:size(toy,3)],NearestNeighbors.Euclidean())
ERROR: MethodError: no method matching length(::Type{SubArray{Float64,2,Array{Float64,3},Tuple{Base.Slice{Base.OneTo{Int64}},UnitRange{Int64},Int64},true}})
Closest candidates are:
  length(::Core.SimpleVector) at essentials.jl:561
  length(::Base.MethodList) at reflection.jl:801
  length(::Core.MethodTable) at reflection.jl:875
  ...
Stacktrace:
 [1] NearestNeighbors.TreeData(::Array{SubArray{Float64,2,Array{Float64,3},Tuple{Base.Slice{Base.OneTo{Int64}},UnitRange{Int64},Int64},true},1}, ::Int64) at [...]/src/tree_data.jl:14
 [2] #BallTree#18(::Int64, ::Bool, ::Bool, ::Array{SubArray{Float64,2,Array{Float64,3},Tuple{Base.Slice{Base.OneTo{Int64}},UnitRange{Int64},Int64},true},1}, ::Type, ::Array{SubArray{Float64,2,Array{Float64,3},Tuple{Base.Slice{Base.OneTo{Int64}},UnitRange{Int64},Int64},true},1}, ::Distances.Euclidean) at [...]/src/ball_tree.jl:39
 [3] NearestNeighbors.BallTree(::Array{SubArray{Float64,2,Array{Float64,3},Tuple{Base.Slice{Base.OneTo{Int64}},UnitRange{Int64},Int64},true},1}, ::Distances.Euclidean) at [...]/src/ball_tree.jl:37
 [4] top-level scope at none:0

While length is defined on SubArray it doesn't seem to be available for ::Type{SubArray[...]} and I'm not sure how and when this creeps up.
I would think creating trees on views would be desirable.

[KristofferC]

We could maybe support this but I will close this since it is a duplicate of #85.