Python 以指定的概率選取元素

Python 以指定的概率選取元素

Problem

You want to pick an item at random from a list, just about as random.choice does, but you need to pick the various items with different probabilities given in another list, rather than picking any item with equal probability as random.choice does.

Solution

Module random in the standard Python library offers a wealth of possibilities for generating and using pseudo-random numbers, but it does not offer this specific functionality, so we must code it as a function of our own:

import random 

def random_pick(some_list, probabilities): 
    x = random.uniform(0,1) 
    cumulative_probability = 0.0 
    for item, item_probability in zip(some_list, probabilities): 
         cumulative_probability += item_probability 
         if x < cumulative_probability:
               break 
    return item 

 

random.uniform(0,1)->生成0.0到1.0之間的偽隨機數,之后循環元素及其概率,計算累積概率.

如：random_pick([1,2,3,4],[0.1,0.2,0.3,0.4])

當x處於0.0到0.1之間,則輸出1

當x處於0.1到0.3之間,則輸出2

……

 

Example

#以指定的概率獲取元素 以一個列表為基准概率，從一個列表中隨機獲取元素 

import random 

def random_pick(some_list, probabilities): 
x = random.uniform(0,1) 
cumulative_probability = 0.0 
for item, item_probability in zip(some_list, probabilities): 
cumulative_probability += item_probability 
if x < cumulative_probability:break 
return item 

some_list = [1,2,3,4] 
probabilities = [0.2,0.1,0.6,0.1] 

print random_pick(some_list,probabilities) 

 

【注意】要求 some_list 的長度和 probabilities 的長度一致,以及所有元素的概率相加為1.0

 

【References】

[1] Randomly Picking Items with Given Probabilities

[2] Python 以指定概率獲取元素