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pythonnumpycumsum
Christopher Flach
Christopher Flach

Reputation: 85

Cumulative Sum List

I'm trying to create a cumulative list, but my output clearly isn't cumulative. Does anyone know what I'm doing wrong? Thanks

import numpy as np
import math
import random

l=[]
for i in range (50):
    def nextTime(rateParameter):
        return -math.log(1.0 - random.random()) / rateParameter
    a = np.round(nextTime(1/15),0)
    l.append(a)
np.cumsum(l)
print(l)

Upvotes: 0

Views: 1596

Answers (2)

AChampion
AChampion

Reputation: 30268

If you are using numpy then numpy is the way to go, however, if all you need to do is provide a cumulative sum then Python3 comes with itertools.accumulate:

def nextTime(rateParameter):
    while True:
        yield -math.log(1.0 - random.random()) / rateParameter

>>> list(it.accumulate(map(round, it.islice(nextTime(1/15), 50))))
[2, 9, 14, 26, 27, ...]

Upvotes: 0

Moses Koledoye
Moses Koledoye

Reputation: 78554

The cumulative sum is not taken in place, you have to assign the return value:

cum_l = np.cumsum(l)
print(cum_l)

You don't need to place that function in the for loop. Putting it outside will avoid defining a new function at every iteration and your code will still produce the expected result.

Upvotes: 1

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