You could implement:
Base.getindex(U::UniformScaling, I::AbstractArray, j::Int) = [U[i,j] for i
in I]
Base.getindex(U::UniformScaling, i::Int, J::AbstractArray) = [U[i,j] for j
in J]
Base.getindex(U::UniformScaling, I::AbstractArray, J::AbstractArray) = [U[i,
j] for i in I, j in J]
Then:
julia> I[1:4, 2]
4-element Array{Int64,1}:
0
1
0
0
On Friday, September 9, 2016 at 11:58:44 AM UTC-5, Steven G. Johnson wrote:
>
> On Friday, September 9, 2016 at 11:56:58 AM UTC-4, Christoph Ortner wrote:
>>
>> I predict that - right now - somebody is writing an answer explaining why
>> this is terrible and you need an abstract array type with lazy evaluation.
>> ;)
>
>
> Well, we already have the built-in constant I. I[i,j] is the j-th
> element of the i-th unit vector, computed lazily, i.e. the Kronecker delta
> function.
>
> But yes, if you need unit vectors a lot you may be doing something wrong.
>
