CODEWITHSUNDEEP
pythonmultiprocessing
Ipulatov
Ipulatov

Reputation: 195

How do I use multiprocessing.Pool on an array?

I have a simple function to use on an array, but when I use multiprocessing.Pool with the function and array, I get the error message "tuple index out of range". How do I fix it?

import numpy as np
import multiprocessing
var1 = 4

array = np.zeros((var1, var1))
    for i in range(np.size(array,1)):
        array[i,0] = 1

def function(array):
    for i in range(np.size(array,1)):
        for t in range( np.size(array,0) - 1):
            array[i,t+1] = array[i,t] + 1
    return(array)

from multiprocessing import Pool

if __name__ == '__main__':
    pool = Pool(processes=2)
    print(pool.map(function, array))

I expect to see a 4x4 array where each row is: 1 2 3 4.

Upvotes: 2

Views: 737

Answers (1)

atline
atline

Reputation: 31584

If not use pool.map, the array which the function get is:

[[1. 0. 0. 0.]
 [1. 0. 0. 0.]
 [1. 0. 0. 0.]
 [1. 0. 0. 0.]]

If use pool.map, the array which the function get is:

[1. 0. 0. 0.]

So, you should not use the same logic to handle array in function just like not use pool.map.

map(func, iterable[, chunksize=None])

You need to use like follows:

import numpy as np
import multiprocessing
var1 = 4

array = np.zeros((var1, var1))
for i in range(np.size(array,1)):
    array[i,0] = 1

def function(array):
    for i in range(np.size(array) - 1):
        array[i+1] = array[i] + 1
    return(array)

from multiprocessing import Pool

if __name__ == '__main__':
    pool = Pool(processes=2)
    print(pool.map(function, array))

Upvotes: 1

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