Python Genetic Algorithm "Natural" Selection

Question

How can I perform selection (i.e. deletion of elements) in an array that tends towards lower numbers.

If I have an array of fitnesses sorted lowest to highest, how can I use random number generation that tends towards the smaller numbers to delete those elements at random.

pop_sorted_by_fitness = [1, 4, 10, 330]

I want to randomly delete one of those smaller elements, where it's most of the time 1, sometimes 4, and rarely 10, with almost never 330. How can I achieve this sort of algorithm.

Possible duplicate of How do I simulate biased die in python? — SiHa
– SiHa, Commented Sep 21, 2017 at 6:53
That's slightly the point it's supposed to favor survival of the "fittest" but still uses RNG to select an array index. — Zavax
– Zavax, Commented Sep 21, 2017 at 6:54
Yeah, sorry, the comment was a bit snarky. Still, a search for Python biased random yields quite a few hits. — SiHa
– SiHa, Commented Sep 21, 2017 at 6:58

Unni · Accepted Answer · 2017-09-21 07:32:06Z

2

How about making use of exponential distribution for sampling your indexes using numpy.random.exponential

import numpy as np 

s = [1, 4, 10, 330] 
limit = len(s)
scale = 10**int(np.log10(limit))
index = int(np.random.exponential()*scale)%limit

Test it

In [37]: sorted([int(np.random.exponential()*scale)%limit for _ in xrange(20)]) 
Out[37]: [0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 2, 3, 3]

edited Sep 21, 2017 at 7:32

answered Sep 21, 2017 at 6:59

Unni

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