Python - shuffle only some elements of a list

Question

I\'m trying to shuffle only elements of a list on 3rd till last position so the 1st two will always stay in place e.g.

list = [\'a?\',\'b\',\'c\',\'d\',\'e\'         


        

Answer 1

I copied the shuffle function from random.shuffle and adapted it, so that it will shuffle a list only on a defined range:

import random
a = range(0,20)
b = range(0,20)

def shuffle_slice(x, startIdx, endIdx):
    for i in reversed(xrange(startIdx+1, endIdx)):
       # pick an element in x[:i+1] with which to exchange x[i]
       j = random.randint(startIdx, i)
       x[i], x[j] = x[j], x[i]

#Shuffle from 5 until the end of a
shuffle_slice(a, 5, len(a))    
print a

#Shuffle b from 5 ... 15
shuffle_slice(b, 5, 15)
print b

The code above only shuffles the elements within the specified range. The shuffle is done inplace, i.e. no copy of the list is created.