[julia-users] Re: Random Set element?

[Steven G. Johnson]

I think you have to use the internals of the Set implementation to have an 
O(1) algorithm here.   For example, the following seems to work:

import Base: GLOBAL_RNG, isslotfilled, rand
function rand(r::AbstractRNG, s::Set)
    isempty(s) && throw(ArgumentError("set must be non-empty"))
    n = length(s.dict.slots)
    while true
        i = rand(r, 1:n)
        isslotfilled(s.dict, i) && return s.dict.keys[i]
    end
end
rand(s::Set) = rand(Base.GLOBAL_RNG, s)


Something like this should probably be in Base.  This could make a good PR 
if you want to add a test case, documentation, etc.