如何添加或增加Python Counter类的单个项目 [英] How to add or increment single item of the Python Counter class

问题描述

一个集合使用 .update 添加多个项目，并使用 .add 添加一个。

A set uses .update to add multiple items, and .add to add a single one.

为什么不 collections.Counter 是否以相同的方式工作？

Why doesn't collections.Counter work the same way?

要递增单个使用 Counter.update 的 Counter 项，您必须将其添加到列表中：

To increment a single Counter item using Counter.update, you have to add it to a list:

from collections import Counter

c = Counter()
for item in something:
    for property in properties_of_interest:
        if item.has_some_property: # simplified: more complex logic here
            c.update([item.property])
        elif item.has_some_other_property:
            c.update([item.other_property])
        # elif... etc

我可以得到计数器就像 set 一样（即消除了将属性放入列表中的行为）？

Can I get Counter to act like set (i.e. eliminate having to put the property in a list)?

用例： C nter 非常好，因为其类似 defaultdict 的行为，即在以后检查时为丢失的密钥提供默认的零：

Use case: Counter is very nice because of its defaultdict-like behavior of providing a default zero for missing keys when checking later:

>>> c = Counter()
>>> c['i']
0

我发现自己正在做很多事情，各种 has_some_property 检查的逻辑（尤其是在笔记本中）。因此，列表理解并不总是那么理想。

I find myself doing this a lot as I'm working out the logic for various has_some_property checks (especially in a notebook). Because of the messiness of that, a list comprehension isn't always desirable etc.

推荐答案

嗯，您并不需要使用 Counter 的方法进行计数，对吗？有一个 + = 运算符，它也可以与Counter一起使用。

Well, you don't really need to use methods of Counter in order to count, do you? There's a += operator for that, which also works in conjunction with Counter.

c = Counter()
for item in something:
    if item.has_some_property:
        c[item.property] += 1
    elif item.has_some_other_property:
        c[item.other_property] += 1
    elif item.has_some.third_property:
        c[item.third_property] += 1

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