Count numbers in python loop

Question

I am trying to get a loop which will tell me the number of 0 in a array of 50 random intergers from 0 to 2 (not including 2). And which will then calculate random integers again for the number of zeroes obtained.

I tried doing it but I am getting stuck at the primary stages and it is getting frustrating so any help would be much appreciated.

from numpy.random import randint

n = 50

R = randint(0,2,n)

for i in R:
    True = 0
    print array(True)

But it doesn't return an array and I don't know how to count the number of 0's as I can't use the len function as I normally would.

I tried using the while loop as well but ran into similar problems

georg · Accepted Answer · 2012-10-28 21:29:42Z

4

Since your array contains only ones and zeroes, the count of zeroes will be obviously

num_zeroes = len(R) - sum(R)

answered Oct 28, 2012 at 21:29

georg

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Comments

arshajii · Accepted Answer · 2012-10-28 21:51:11Z

2

To count the 0s in R you can just do

sum(not n for n in R)

The advantage of this is that it will work even if you have numbers other than only 1s and 0s in the array.

Thanks to eryksun for pointing this out: you can also do

numpy.sum(R == 0)

edited Oct 28, 2012 at 21:51

answered Oct 28, 2012 at 21:23

arshajii

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2 Comments

Eryk Sun Over a year ago

Vectorized: numpy.sum(R == 0).

arshajii Over a year ago

@user1778543 Sure - not n returns 1 if n is 0 and it returns 0 otherwise. not n for n in R: we loop over R and calculate not n for each element n, we then simply add these values with sum to obtain the total number of 0s.

Uri London · Accepted Answer · 2012-10-28 21:43:41Z

0

Generating the array:

random_list = [random.randint(0,2) for x in xrange(50)]

number of 0's:

num_zeros = sum( 1 for x in random_list if x==0 )

generating the array again:

random_list = [random.randint(0,2) for x in xrange(num_zeros)]

answered Oct 28, 2012 at 21:43

Uri London

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Comments

Akavall · Accepted Answer · 2012-10-28 22:04:54Z

0

Perhaps this is something you are looking for:

from numpy.random import randint

n = 50

R = randint(0,2,n)

def get_number_of_zeros(x):
    return sum(0 == ele for ele in x)

while(len(R) > 0):
    number_of_zeros = get_number_of_zeros(R)
    print 'number of zeros is {}'.format(number_of_zeros)
    R = randint(0, 2, number_of_zeros)

Result:

number of zeros is 25
number of zeros is 11
number of zeros is 7
number of zeros is 4
number of zeros is 1
number of zeros is 1
number of zeros is 1
number of zeros is 0

answered Oct 28, 2012 at 22:04

Akavall

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Comments

alexis · Accepted Answer · 2016-06-09 20:54:45Z

0

Hmm, no need for loops and sums. If you have an array of integers, you can count the number of zeros (or any other individual number) like this:

>>> R = [ 0, 1, 5, 0, 0]
>>> print("There are", R.count(0), "zeros")
There are 3 zeros

answered Jun 9, 2016 at 20:54

alexis

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