## How to optimize data generation for numpy call

Question

I'd like to know how to make the following code shorter and/or more efficient. Could I (or should I) get rid of the for loop by using a functional method, or is there method I should be using from numpy?

The code calculates the expected value of an array of of integers.

``````vals = np.arange(self.n+1)

# array of probability of each value in vals
parr = np.ones(len(vals))
for i in range(len(vals)):
parr[i] *= self.prob(vals[i])

return np.dot(vals,parr)
``````

As requested in comments, the implementation of the method prob():

``````def prob(self, x):

"""Computes probability of removing x items

:param x: number of items to remove
:returns: probability of removing x items
"""

# p is the probability of removing an item
# sl.choose computes n choose x
return sl.choose(self.n, x) * (self.p**x) * \
(1-self.p)**(self.n-x)
``````

Show source

## Answers to How to optimize data generation for numpy call ( 2 )

1. The loop can be reduced to a list comprehension:

``````vals = np.arange(self.n+1)

# array of probability of each value in vals
parr = [self.prob(v) for v in vals]

return np.dot(vals, parr)
``````
2. I think it will be most faster:

``````vals = np.arange(self.n+1)

# array of probability of each value in vals
parr = self.prob(vals)

return np.dot(vals,parr)
``````

and function:

``````def prob(list_of_x):

"""Computes probability of removing x items

:param list_of_x: numbers of items to remove
:returns: probability of removing x items
"""

# p is the probability of removing an item
# sl.choose computes n choose x
return np.asarray([sl.choose(self.n, e) for e in list_of_x]) * (self.p ** list_of_x) * \
(1-self.p)**(self.n - list_of_x)
``````

Because numpy is faster:

``````import timeit

import numpy as np

list_a = [1, 2, 3] * 1000
list_b = [4, 5, 6] * 1000

np_list_a = np.asarray(list_a)
np_list_b = np.asarray(list_b)

print(timeit.timeit('[a * b for a, b in zip(list_a, list_b)]', 'from __main__ import list_a, list_b', number=1000))
print(timeit.timeit('np_list_a * np_list_b', 'from __main__ import np_list_a, np_list_b', number=1000))
``````

Result:

``````0.19378583212707723
0.004333830584755033
``````