Selections refactor

[aahaselgrove]

Refactored selections.jl to fix some bugs (including issue #40) and improve clarity.

[coveralls]

Coverage decreased (-22.5%) to 77.511% when pulling 340e307 on aahaselgrove:selections_refactor into c7fb224 on wildart:master.

[aahaselgrove]

Separated out this change from others so it may be considered independently.

[aahaselgrove]

I can see that this change has broken the new selections.jl tests. Could you please explain what uniformranking is meant to do? My understanding of a 'uniform' selection is that each individual has an equal change of being selected. As the sum of probabilities must equal 1, your current implementation and tests don't make sense to me.

[wildart]

It isn't just uniform, it is (μ, λ)-uniform ranking which takes μ fittest individuals and selects uniformly from them. λ is a total number of individuals in the population. If you want a uniform selection you need to make that μ = λ.

I test the following:

s = uniformranking(2)
s([1,2,3], 2) == [2,3]

s is the selection function which takes two fittest individuals that are in position 2 & 3 of the first parameters and then selects uniformly from them. I think the better test would be

sort(unique(s([1,2,3], 10))) == [2,3]

It wouldn't rely on RNG settings.

[aahaselgrove]

I don't think that removed the dependency on RNG settings, as the selector still chooses randomly. eg. in your example [2, 2] and [3, 3] would be equally valid results.