如何从python列表中随机选择一对相邻元素

Question

What is the best way to select randomly two adjacent elements from a list?

As for example, for a given list M=[2,0,8,6,4,0,1,2,4,6,5,6,5,89,12,23] Suppose I would like to select elements like (2,0),(6,5),(89,12),(5,89),(0,8) etc. Here is the code I have tried :

import random
D=[]
M=[2,0,8,6,4,0,1,2,4,6,5,6,5,89,12,23]
  for r in range(10):
  D.append((random.sample(M,2)))

But it does not give the right pairs

Answer 1

Use the length of the list as a limit for a random integer then use it as an index into the list, also select the next item.

>>> a =[2,0,8,6,4,0,1,2,4,6,5,6,5,89,12,23]
>>> n_pairs = 6
>>> for _ in range(n_pairs):
...     i = random.randrange(len(a)-1)
...     print(a[i], a[i+1])

6 5
89 12
5 89
2 4
5 6
12 23

>>> 

---

Without repeats:

>>> a =[2,0,8,6,4,0,1,2,4,6,5,6,5,89,12,23]
>>> n_pairs = 6
>>> if n_pairs > len(a)//2:
    raise ValueError

>>> indices = random.sample(range(len(a)), n_pairs)
>>> result = [(a[i], a[i+1]) for i in indices]
>>> result
[(2, 0), (0, 8), (6, 5), (6, 5), (5, 89), (89, 12)]

Answer 2

So, try this:

import random
D=[]
M=[2,0,8,6,4,0,1,2,4,6,5,6,5,89,12,23]
for r in range(10):
    idx = random.randint(0, len(M) - 2)
    D.append((M[idx], M[idx+1]))

Answer 3

If your M is small and your adjacent pair should strictly be in the same order as M, first form the value pair list and then choose one from that list:

In [1]: M=[2,0,8,6,4,0,1,2,4,6,5,6,5,89,12,23]

In [2]: N = [(i, j) for i, j in zip(M[:-1], M[1:])]

In [3]: N
Out[3]:
[(2, 0),
 (0, 8),
 (8, 6),
 (6, 4),
 (4, 0),
 (0, 1),
 (1, 2),
 (2, 4),
 (4, 6),
 (6, 5),
 (5, 6),
 (6, 5),
 (5, 89),
 (89, 12),
 (12, 23)]

In [4]: import random

In [5]: random.choice(N)
Out[5]: (2, 4)

If you want the list in a shuffled order and want 6 pairs:

In [3]: random.shuffle(N)

In [4]: N[:6]
Out[4]:
[(89, 12),
 (0, 8),
 (6, 4),
 (2, 4),
 (2, 0),
 (6, 5)]

Answer 4

This appears to give the proper results. I did edit an above answer to get the proper results.

import random
D=[]
M=[2,0,8,6,4,0,1,2,4,6,5,6,5,89,12,23]
for r in range(10):
    try:

        idx = random.randint(0, len(M))
        D.append((M[idx], M[idx + 1]))
        print(D)
    except:
        print('Error')