I need to generate a randomly filled fix-sized list of integers using only some predefined numbers to choose from. Also, the sum of the numbers in this new list has to be equal to a given number.
For example: randomly repeat these 3 numbers -2, 2, 3 to create a new list with size 20 and the sum of list items has to be 60. In this example, size = 20, sum = 60, and numbers = [-2, 2, 3] are inputs.
Can I do this in python?
import numpy as np
def sum_to_x(n, x):
values = [0.0, x] + list(np.random.uniform(high=x, size=n - 1))
values.sort()
return [values[i + 1] - values[i] for i in range(n)]
d = sum_to_x(20, 60)
print(d)
print(sum(d))
output:
[1.1666321716192374, 3.7356682360404636, 0.10213495009527396, 15.944355221343475, 4.823749563474106, 2.771274835477797, 1.1543877569990038, 6.6231006904687675, 1.0517272997350275, 6.954578248764335, 0.9446793094979142, 2.079080332702951, 1.1813248101489293, 3.3584697034830597, 0.8048689399051554, 1.3952223726127002, 4.797652596772288, 0.30201710006423355, 0.5143495684426824, 0.29472629235259973]
60.0
for integer values:
import random as r
def random_sum_to(n, num_terms=None):
num_terms = (num_terms or r.randint(2, n)) - 1
a = r.sample(range(1, n), num_terms) + [0, n]
list.sort(a)
return [a[i + 1] - a[i] for i in range(len(a) - 1)]
print(random_sum_to(60, 20))
output:
[3, 3, 4, 1, 2, 5, 4, 1, 4, 2, 1, 2, 1, 2, 1, 3, 6, 1, 12, 2]
60
You can do it, but you should know that this is a complex problem to solve it in optimal time.
I can only give you a random solution, which may take a lot of time in some cases, because it is, you know, random:
import random
def create_list(possible_values, size, sum_of_values, max_iterations=10**5):
for i in range(max_iterations):
values = [
random.choice(possible_values)
for _ in range(size)]
if sum(values) == sum_of_values:
# only exit once it reaches the goal
print('solution found after {:,d} iterations'.format(i))
return values
raise ValueError(
'no solution found after {:,d} iterations'.format(max_iterations))
Here is a demonstration; the same parameters may have a different durations in each invocation of the function
>>> create_list([-1, 0, 1, 2, 3], 20, 30)
solution found after 38 iterations
[1, 2, 1, 1, 1, 3, 2, 2, 3, 2, 3, 2, 1, 1, -1, 0, 0, 2, 2, 2]
>>> create_list([-1, 0, 1, 2, 3], 20, 30)
solution found after 31 iterations
[2, 2, 3, 0, 3, 1, 1, 1, 3, 3, 1, 1, 0, 2, 1, -1, 3, 3, 0, 1]
>>> create_list([-1, 0, 1, 2, 3], 20, 30)
solution found after 93 iterations
[2, -1, 2, 1, 3, 2, -1, 0, 2, -1, 3, 3, 2, 2, 3, 1, 1, 0, 3, 3]
>>> create_list([-1, 0, 1, 2], 20, 30)
solution found after 50,456 iterations
[1, 2, 2, 2, 2, 2, 2, 2, -1, 2, 1, 0, 2, 2, 2, 2, 2, 0, 2, 1]
If it fails, you can try again with a higher number of iterations, but it does not always solve the issue:
>>> create_list([-1, 0, 1], 20, 30)
Traceback (most recent call last):
File "<input>", line 1, in <module>
File "/home/ralf/PycharmProjects/django_test_02/run_pw.py", line 20, in create_list
'no solution found after {:,d} iterations'.format(max_iterations))
ValueError: no solution found after 100,000 iterations
>>> create_list([-1, 0, 1], 20, 30, 10**6)
Traceback (most recent call last):
File "<input>", line 1, in <module>
File "/home/ralf/PycharmProjects/django_test_02/run_pw.py", line 20, in create_list
'no solution found after {:,d} iterations'.format(max_iterations))
ValueError: no solution found after 1,000,000 iterations