Scaling an array of occurences in python

Question

I have an array of ints which describes the absolute occurrence of unique items in a data set. eg. a = [5, 3, 1] means there are three unique items with a data set length of 9, perhaps x y and z, and they occur

x -> 5 times
y -> 3 times
z -> once

How can I "stretch" array a to a smaller or larger sized int array by maintaining proportions between the ints? Since exact proportions can't be maintained, I think about rounding things up, eg an array of 3 items shrunk from a would look like:

x -> 2 times
y -> once
z -> none (because it's the least probable to occur in the original array)

Answer 1

You could use list multiplying. Let me know if this example is enough for you to continue with your work.

from collections import Counter
from math import ceil

init_list = [3, 4, 5, 5, 5, 4, 4, 4]

occur_dict = Counter(init_list)
new_length = 20

old_length = len(init_list)
new_occur_dict = {num: ceil(occur / old_length * new_length)
                  for (num, occur) in occur_dict.items()}
# new occurrences dict, rounded up so sum should be bigger than new _length

sorted_nums = [num for (num, occur) in sorted(occur_dict.items(),
                                              key=lambda x: x[1])]
# sorting keys by occurrences, so lowest number will be first
while sum(new_occur_dict.values()) > new_length:
    for number in sorted_nums:
        new_occur_dict[number] -= 1 #removing extra occurrences to match new_length
        if sum(new_occur_dict.values()) == new_length:
            break

new_list = []
for item in occur_dict:
    new_list += [item] * new_occur_dict[item]