Creating a random list from a list without repeating items

Question

I am trying to create a new list of lists from a list. The goal is to randomly pick a name from listA and add it in a specific spot in listB. However, names should not be repeated in listB.

Here is my attempt. Sometimes it works and other times I get "RecursionError: maximum recursion depth exceeded in comparison". It traces back to yFinder or zFinder.

Any advice would be appreciated. Thanks!

import random

listA = ["Foo","Spam","Eggs"]
listB = [["A"],["B"],["C"]]

x = random.sample(listA,1)
y = random.sample(listA,1)
z = random.sample(listA,1)

def xFinder():
  x
  listB[0].append(x)

def yFinder():
  y
  if y != x:
    listB[1].append(y)
  else:
    yFinder()

def zFinder():
  z
  if z == y:
    zFinder()
  elif z == x:
    zFinder()
  else:
    listB[2].append(z)   

xFinder()
yFinder()
zFinder()

print(listB)

When `y == x`, `yFInder()` recurses infinitely, since you never change `x` or `y` when it calls itself. — Barmar, Jan 02 '20 at 07:06
And `zFinder()` recurses infinitely if `z` is the same as `x` or `y`. — Barmar, Jan 02 '20 at 07:07
Thanks for the answers. I am new to coding so recursion is still something I need to figure out. Clearly. What I was hoping is that by running the loop again a new name would appear from listA which would make yFinder or zFinder True and append a different name. — Alroc, Jan 02 '20 at 07:12
I suspect you expected the line `y` to reassign `y` randomly. It doesn't. — Barmar, Jan 02 '20 at 07:13
You don't need to use recursion here. Just shuffle `listA`, then append `listA[0]` to `listB[0]`, append `listA[1]` to `listB[1]`, etc. — Barmar, Jan 02 '20 at 07:14
@Belmar. Exactly. so you're saying it will choose the same name? — Alroc, Jan 02 '20 at 07:14
you can use shuffle() from random. `random.shuffle(list1)` and add each element in list2. `for i in list1: list2.append([i])`. — Ch3steR, Jan 02 '20 at 07:15
Thank you @Barmar. Shuffle is a simpler solution to my problem. — Alroc, Jan 02 '20 at 18:34
Thanks @Ch3steR. It is a much simpler solution to my problem. — Alroc, Jan 02 '20 at 18:34
@Ch3steR That's not correct. You need to append to the corresponding element, and you shouldn't be putting `i` in a list. — Barmar, Jan 02 '20 at 20:54

score 1 · Accepted Answer · answered Jan 02 '20 at 20:55

You're getting infinite recursion because you never reassign any of the variables when you call the functions recursively. So the same if condition succeeds, and you recurse again.

But picking a random element repeatedly is not a good way to do this. Shuffle list1, then append each element of list1 to the corresponding element of list2.

random.shuffle(list1)
for i, el in enumerate(list1):
    list2[i].append(el)

Creating a random list from a list without repeating items

1 Answers1