python - How to shuffle an array of numbers without two consecutive elements repeating?

Question

I'm currently trying to get an array of numbers like this one randomly shuffled:

label_array = np.repeat(np.arange(6), 12)

The only constrain is that no consecutive elements of the shuffle must be the same number. For that I'm currently using this code:

# Check if there are any occurrences of two consecutive 
# elements being of the same category (same number)
num_occurrences = np.sum(np.diff(label_array) == 0)

# While there are any occurrences of this...
while num_occurrences != 0:
    # ...shuffle the array...
    np.random.shuffle(label_array)

    # ...create a flag for occurrences...
    flag = np.hstack(([False], np.diff(label_array) == 0))
    flag_array = label_array[flag]

    # ...and shuffle them.
    np.random.shuffle(flag_array)

    # Then re-assign them to the original array...
    label_array[flag] = flag_array

    # ...and check the number of occurrences again.
    num_occurrences = np.sum(np.diff(label_array) == 0)

Although this works for an array of this size, I don't know if it would work for much bigger arrays. And even so, it may take a lot of time.

So, is there a better way of doing this?

Answer 1

May not be technically the best answer, hopefully it suffices for your requirements.

import numpy as np
def generate_random_array(block_length, block_count):
    for blocks in range(0, block_count):
        nums = np.arange(block_length)
        np.random.shuffle(nums)
        try:
            if nums[0] == randoms_array [-1]:
                nums[0], nums[-1] = nums[-1], nums[0]
        except NameError:
            randoms_array = []
        randoms_array.extend(nums)
    return randoms_array


generate_random_array(block_length=1000, block_count=1000)