计算每个键的出现次数答案

【问题标题】：Counting occurence of each key计算每个键的出现次数
【发布时间】：2021-05-25 18:21:28
【问题描述】：

我有以下用户

users = [
  { username: "user1", state: "USA" },
  { username: "user2", state: "Canada" },
  { username: "user3", state: "China" },
  { username: "user4", state: "China" },
  { username: "user4", state: "USA" },
];

我想计算每个状态的出现次数并将其连同其值一起打印出来。我的输出应该是这样的

USA, 2
Canada,1
China,2

我在 python 中使用了计数器，但遇到了问题。

users = [
  { username: "user1", state: "USA" },
  { username: "user2", state: "Canada" },
  { username: "user3", state: "China" },
  { username: "user4", state: "China" },
  { username: "user4", state: "USA" },
];
from collections import Counter

counts = Counter(c for c in 'users' if c in 'USA, Canada, China')
for k,v in counts.iteritems():
    print(k,v)

【问题讨论】：

您面临哪些问题？
name 'username' not defined 是错误
.iteritems() 是一个 python 2.7 函数。已重命名为.items()
@12944qwerty 感谢您的帮助

标签： python python-3.x counter

【解决方案1】：

语法{ username: "user1", state: "USA" }, 仅适用于javascript，在python 中，您也需要在键周围加上引号：{"username": "user1", "state": "USA" },

你还迭代'users'，这是一个字符串，你需要使用你的变量users，然后用c['part']取状态部分

from collections import Counter

users = [
    {"username": "user1", "state": "USA"}, {"username": "user2", "state": "Canada"},
    {"username": "user3", "state": "China"}, {"username": "user4", "state": "China"},
    {"username": "user4", "state": "USA"},
]
counts = Counter(c['state'] for c in users)

for k, v in counts.items():
    print(k, v)

# iterate on descending count order
for k, v in counts.most_common():
    print(k, v)

【讨论】：