how to shuffle a binary array a specific amount

Question

I have a binary array. I want to shuffle it such that n percent of random elements stay in the same place and the rest get shuffled. Another way of putting it is, I have a binary array and I want to create a second array that is of same length and n percent similar when compared to the first using difflib

I'm using random.shuffle to shuffle the array but can't find info on the percent part of my question.

import random

array = [1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0]
random.shuffle(array)
print(array)

James · Accepted Answer · 2019-08-23 19:52:42Z

1

If you are open to using numpy, you can create a boolean mask to pull approximately n-fraction of the arr, shuffle the pulled sample, then put the shuffled result back into the masked locations.

import numpy as np

n = 0.2
arr = np.array([1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0])

# create boolean mask of about fraction n
ix = np.random.choice([True, False], size=arr.size, replace=True, p=[n, 1-n])

# pull the masked portion and shuffle
arr_shuff = arr[ix]
np.random.shuffle(arr_shuff)

# reinsert
arr[ix] = arr_shuff

arr
# returns:
array([1, 1, 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0])

edited Aug 23, 2019 at 19:52

answered Aug 23, 2019 at 19:43

James

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4 Comments

badam Over a year ago

i get the error AttributeError: module 'numpy' has no attribute 'shuffle' when testing this code but np.random.shuffle seems to work

James Over a year ago

oops. it is supposed to be np.random.shuffle. fixed now

badam Over a year ago

This may be a separate question, but if I want to use this code to return several shuffled arrays (all different, but based on the same initial array) how might I do it? When using a for loop I get the same shuffled array several times for i in range(10): print(arr)

James Over a year ago

Wrap up the code into a function that takes an array as an input. The first line of function would be to create a copy of the array using arr.copy(), then perform the operations on the copy so as to not change the original array

Kfir Dadosh · Accepted Answer · 2019-08-23 19:50:42Z

0

I don't think you would find a standard function for this. You can swap n * len(array) with other items in the array:

import random

array = [1,1,1,1,1,1,1,1,1,1,0,0,0,0,0,0,0,0,0,0]
n = 0.2

for i in range(int(n*len(array))):
    ri = random.randrange(len(array))
    array[i], array[ri] = array[ri], array[i]

print(array)

however, if the array is filled with only zero's or one's you will get no diff.

answered Aug 23, 2019 at 19:50

Kfir Dadosh

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