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，该函数返回一个字典，其中项目计数为键，以及具有该计数的项目列表。

以下是测试用例的示例: 输入:{'x':3，'y':3，'z':100} 输出:{3: ['x', 'y'], 100: ['z']}

这是我到目前为止的代码:

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创建相应的列表？

感谢您的帮助!

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']}