Sorting based on two variables in python

Question

I am writing a sorting algorithm in Python.

For example,

Lets say I have 10 child generated from 1 parent. Each child has two attributes "Fitness" and "Noise".

Lets say, I calculate the "Fitness" for 10 children first and select only the 3 best children (higher "fitness" are chosen as best). For example let us take 60,50,40 as fitness values for the 3 best children.

Now I proceed to calculate the "noise" of the 3 children. Again for example, lets assume I get the "noise" for 3 children as 5,8,6. (Less "noise" is considered better).

How do I find a sorting algorithm to choose based on best "fitness" and "noise". I would ideally require a child with high "fitness" and low "noise". I would need to sort them in a way I take the best child out of 3 children.

Initial 3 children:

Fitness {60,50,40} Noise {5,8,6}

My Ideal 3 children after sorting should be:

Fitness {60,40,50} Noise {5,6,8}

I am also not sure how to give the weighting for selecting noise as a secondary variable.

Basically I am looking for a good sorting algorithm in python.

So you want to sort on 2 keys, first one descending and second one ascending? What is your data set? structure and values — Tim
– Tim, Commented Jun 18, 2015 at 13:33
It would be easy to do "sort by fitness descending, using noise ascending as a tie-breaker" but if you want fitness 40 noise 6 to be higher than fitness 50 noise 8, then you will have to write an equation that takes both fitness and noise and returns a single number indicating the child's overall value. There's no built-in way to do this; you will have to play around with the arithmetic until you get results that look good to you. — Kevin
– Kevin, Commented Jun 18, 2015 at 13:35
perhaps the "in Python" is a red herring. first try to figure out the algorithm, and once you've figured it out, then try to implement it. — hakamadare
– hakamadare, Commented Jun 18, 2015 at 13:39
@Kevin .. This seems to be a good Idea. Take a Overall value between Fitness and Noise as a single number and compare the results. — Balaji Spades
– Balaji Spades, Commented Jun 18, 2015 at 14:05

Open AI - Opting Out · Accepted Answer · 2015-06-18 14:15:05Z

4

>>> from collections import namedtuple

>>> Child = namedtuple('Child', 'fitness noise')

>>> children = [Child(fitness=60, noise=5),
...             Child(fitness=50, noise=8),
...             Child(fitness=40, noise=6)]

You can use the builtin sorted function, and pass a lambda as the key. The lambda returns the object used for comparison. If we return a tuple, it will sort based on the first element of the tuple, then the second, etc.

If we make the tuple first be the noise, then the negative of the fitness, it will give the order you want:

>>> sorted(children, key=lambda child: (child.noise, -child.fitness))
[Child(fitness=60, noise=5),
 Child(fitness=40, noise=6),
 Child(fitness=50, noise=8)]

edited Jun 18, 2015 at 14:15

answered Jun 18, 2015 at 13:36

Open AI - Opting Out

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Utsav T · Accepted Answer · 2015-06-18 13:39:52Z

1

Assuming you have a list of tuples, where each tuple represents the two attributes fitness and noise - [(10,5),(90,7),(100,12) ...], you can use the following piece of code -

>>> l = [(100,5),(89,13),(102,65),(10,3),(109,45)]
>>> l.sort(key = lambda x:x[0], reverse = True) ## Sorting(descending) on the basis of fitness
>>> l_ = l[:3]                                  ## Extract the top 3 tuples
>>> l_.sort(key = lambda x:x[1])                ## Sorting on the basis of noise

answered Jun 18, 2015 at 13:39

Utsav T

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