Averaging over every n elements of an array without numpy

Question

I have an array. I want to create a new array which is the average over every third element. So the new array will be a third of the size as the original.

As an example:

 [1,2,3,1,2,3,1,2,3]

should return the array:

 [2,2,2]

Can anyone suggest an efficient way of doing this? I want to do this without using numpy.

Have a look at the grouper recipe in the itertools documentation: https://docs.python.org/2/library/itertools.html#recipes — Rob, Oct 24 '16 at 11:18
Elegant and efficient way is the one with numpy, that you provided. Others will include manually splitting the array and calculating the mean of it. Would be neither efficient nor elegant. — Dmitry Yantsen, Oct 24 '16 at 11:18

score 1 · Accepted Answer · answered Oct 24 '16 at 11:31

what is the problem?

a = [1,2,3,4,5,6,7,8,9]
def reduce_list(any_list, number_of_values_to_combine):
    ret_list = []
    for i in range(len(any_list)//number_of_values_to_combine):
        new_value = 0
        for j in range(number_of_values_to_combine):
            new_value += any_list[i*number_of_values_to_combine + j]
        ret_list.append(new_value/number_of_values_to_combine)
    return ret_list

print reduce_list(a,3)

rest will be ignored, if there are f.e. 7 elements combined to 3 there will be 2 elements in the result

score 0 · Answer 2 · answered Oct 24 '16 at 11:26

l = [1,2,3,2,1,4,3,2,4,5,6,4,3,1,5]
n = 3
sub = [l[(n-1) + i*n] for i in range(int(len(l)/n))]
avg_every_third_element = sum(sub)/len(sub)

Next time show your effort. Nobody can help you to improve your approach if there is none. And most questions (as yours here) can be solved with a little bit of research.

score 0 · Answer 3 · answered Oct 24 '16 at 11:42

0

a = [1,2,3,1,2,3,1,2,3]
array_result = []

for i in range(a):
    if i%3 == 0:
        new_number = (a[i]+a[i-1]+a[i-2])/3
        array_result.append(new_number)

That worked for me.

answered Oct 24 '16 at 11:42

xgrimau

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Averaging over every n elements of an array without numpy

3 Answers3