Removing two adjacent values from a list randomly

Question

I found the function pop() , which will remove a single value from a list. However, I want to remove two values from the list - randomly, but both numbers must be adjacent. For example, in a list of [1, 2, 3, 4, 5] , if I randomly picked 2 with pop() , I'd also want to remove 1 or 3 .

I need to store the numbers (p and q) for a later calculation, here's my code so far:

nlist = [1, 2, 3, 4, 5]
shuffle(nlist)

while nlist:
    p = nlist.pop(random.randrange(len(nlist)))
    #save p and one adjacent value (q) within this loop
    #remove p and q from list

Answer 1

You could choose the randrange to be across one less than the list's length, and then pop the same index twice:

pop_index = random.randrange(len(nlist)-1)
p = nlist.pop(pop_index)
q = nlist.pop(pop_index)

Answer 2

You need to handle some edge cases when removing your elements, namely when the p is the first or last element in the list. This uses a handy random function, choice to determine which adjacent element you choose.

while len(nlist) > 1:
    # the number to remove
    p_index = random.randrange(len(nlist))
    if p_index == 0:
        q_index = p_index + 1
    elif p_index == len(nlist) - 1:
        q_index = p_index - 1
    else:
        q_index = p_index + random.choice([-1, 1])
    p, q = nlist[p_index], nlist[q_index]
    nlist.pop(p_index)
    nlist.pop(q_index)
    return p, q

Answer 3

You can try this approach:

from random import randint
nlist = [1, 2, 3, 4, 5]
data=randint(0,len(nlist)-2)
print([j for i,j in enumerate(nlist) if i not in range(data,data+2)])

output:

#[3, 4, 5]
#[1, 4, 5]
#[1, 2, 5]