Using view() with map()

[ahwillia]

Is there a way to apply map() to an ArrayView in Julia?

using ArrayViews
A = rand(10,10);
sum(map(x->x>0.5,A[1,:])); # works, gives something reasonable, e.g. 5
sum(map(x->x>0.5,view(A,1,:)))

Using the ArrayView produces the following error

ERROR: `similar` has no method matching similar(::StridedView{Float64,2,0,Array{Float64,2}}, ::Type{Bool}, ::(Int64,Int64))
in similar at abstractarray.jl:116
in map at abstractarray.jl:1329

I also posted this question on stack overflow, but wasn't sure if I should post here as well. Feel free to close this if this isn't the appropriate venue.

[andreasnoack]

I think this is the right place to post this. There ought to be a similar method defined for ArrayViews. It would be great if you could prepare a pull request with this.

[ahwillia]

I can try. This similar method in src/common.jl looks really close to what we want?

similar{T}(a::StridedArrayView{T}, ::Type{T}, dims::Dims) = Array(T, dims)

Are you saying we just to repeat this for StridedView rather than StridedArrayView?

similar{T}(a::StridedView{T}, ::Type{T}, dims::Dims) = Array(T, dims)

Not sure that I understand the distinction between the two.

[andreasnoack]

I think that you should simply remove the {T} part of StridedArrayView{T}. It seems wrong that you can only choose the same element type as the input arrays. Could you try to change that?

[simonster]

StridedArrayView is the supertype of all ArrayViews, so that part is right. But this method is only applicable when the type is the same as the type of the view. I think it should be:

similar{T}(a::StridedArrayView, ::Type{T}, dims::Dims) = Array(T, dims)

I also don't think the other two methods should be necessary since they are defined in Base.

[ahwillia]

Yes, what you suggest works now. What should I do with the other two methods? If I delete the {T} part from those, I get a warning:

Warning: static parameter T does not occur in signature for similar at /home/alex/.julia/v0.3/ArrayViews/src/common.jl:64.
The method will not be callable.

My guess would be this? (Sorry I'm still a bit new to julia)

similar(a::StridedArrayView) = Array(typeof(a), size(a))
similar(a::StridedArrayView, dims::Dims) = Array(typeof(a), dims)
similar{T}(a::StridedArrayView, ::Type{T}, dims::Dims) = Array(T, dims)

[andreasnoack]

Just try to delete them completely. As @simonster said, they should be covered by methods in base.

[ahwillia]

Ok. Deleting them seems to work. Will open a pull request.

julia> using ArrayViews
julia> A = rand(10,10);
julia> similar(view(A,1,:))
1x10 Array{Float64,2}:
 0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0  0.0
julia> similar(view(A,1,:),(2,2))
2x2 Array{Float64,2}:
 0.0  0.0
 0.0  0.0
julia> sum(map(x->x>0.5,view(A,1,:)))
7