python - 如何在 python 3.6 中创建带有值列表的频率字典

Question

我正在尝试在 python 3.6 中编写一个函数，该函数返回一个以项目计数为键的字典和一个具有该计数的项目列表。

下面是一个测试用例的示例： 输入：{'x':3, 'y':3, 'z':100} 输出：{3: ['x', 'y'], 100 ：['z']}

到目前为止，这就是我的代码：

def get_count_items(key_count):
    # create blank dictionary
    count_items = {}
    #for each item_key in key_count:
    for item_key in key_count
    # retrieve its value (which is a count)
    # if the count (as key) exists in count_items:
    if item in count_items:
        count_items[item] += 1
    # append the item_key to the list
    # else:
    #add the count:[item_key] pair to count_items dictionary
    else:
        count_items[item] = 1

    for key, value in count_items.items():
    #return count_items dictionary
        return count_items

我的问题是如何将每个计数值设置为键，以及如何为具有该计数的每个项目制作相应的列表？

谢谢您的帮助！

标签： pythonlistdictionarypython-3.6

Answer 1

from collections import defaultdict

d = {'x':3, 'y':3, 'z':100} 

# create defaultdict with list type. 
res = defaultdict(list)

# iterate over key value pair
for k, v in d.items():
    res[v].append(k)
print(res)
# or
print(dict(res))

输出：

defaultdict(<class 'list'>, {3: ['x', 'y'], 100: ['z']})
{3: ['x', 'y'], 100: ['z']}