How To Randomize The Order Of Elements Of A List While Making Sure No Consecutive Values Are Equal?

I have a python list of strings, let's say: elems = ['A', 'B', 'C', 'D'] I want to create a new list whose elements are each element of elems repeated a fixed number of times (let

Solution 1:

I am assuming that the input list has distinct elements.

import random

defrandomize_carefully(elems, n_repeat=2):
    s = set(elems)
    res = []
    for n inrange(n_repeat):
        if res:
            # Avoid the last placed element
            lst = list(s.difference({res[-1]}))
            # Shuffle
            random.shuffle(lst)
            lst.append(res[-1])
            # Shuffle once more to avoid obvious repeating patterns in the last position
            lst[1:] = random.sample(lst[1:], len(lst)-1)
        else:
            lst = elems[:]
            random.shuffle(lst)
        res.extend(lst)
    return res

for i inrange(10):
    print randomize_carefully(["A", "B", "C", "D"])

Some output:

['B', 'C', 'D', 'A', 'C', 'A', 'D', 'B']['B', 'D', 'C', 'A', 'C', 'B', 'A', 'D']['C', 'B', 'D', 'A', 'B', 'C', 'D', 'A']['B', 'D', 'A', 'C', 'A', 'B', 'D', 'C']['D', 'C', 'A', 'B', 'C', 'D', 'A', 'B']['C', 'D', 'A', 'B', 'D', 'C', 'A', 'B']['D', 'A', 'C', 'B', 'C', 'A', 'B', 'D']['C', 'D', 'A', 'B', 'C', 'D', 'A', 'B']['C', 'B', 'A', 'D', 'A', 'B', 'D', 'C']['B', 'D', 'A', 'C', 'A', 'D', 'C', 'B']

Solution 2:

You could make a function that checks if two consecutive values in a list x are the same:

defcompareConsecutive(x):
    for i in x:
        if i == x[x.index(i)+1]:
            returnFalse

Then shuffle the list in a while loop until compareConsecutive() stops returning False:

whilecompareConsecutive(ans)== False:
    random.shuffle(ans)

This could take a while with a long list, since random.shuffle() could keep generating lists that have consecutive values in them, but it will work eventually :)

Solution 3:

I think this could be an algorithm for doing what you want:

let R be your result list

1. pick a random element e from elems, and append e to R
2. let elems_1 = elems \ e, i.e. remove e from elems
3. pick a random element e_1 from elems_1, and append e_1 to R
4. let elems_1 = elems \ e_1, i.e. remove e_1 from elems
5. repeat from step 3 until R is long enough

Solution 4:

I think this will work, although it is not so elegant.

import random

elems = ['a','b','c','d']
length = len(elems)

l = []

for i in range(2):
    random.shuffle(elems)
    l.extend( elems )
    if i > 0and l[ i*length ] == l[ i*length - 1 ]:
        l[i*length-2], l[i*length-1] = l[i*length-1], l[i*length-2]

print l