Help writing a `collect` for iterators

[juliohm]

Final solution:

function collectat(iter, inds)
  if isempty(inds)
    eltype(iter)[]
  else
    m = maximum(inds)
    e = Iterators.enumerate(iter)
    w = Iterators.takewhile(x -> (first(x) ≤ m), e)
    f = Iterators.filter(x -> (first(x) ∈ inds), w)
    map(last, f)
  end
end