Python pandas pivot_table margins keyError [英] Python pandas pivot_table margins keyError

问题描述

考虑以下数据框:

test = pd.DataFrame({'A': [datetime.datetime.now(), datetime.datetime.now()], 'B': [1, 2]})

如果我像下面那样使用 pivot_table 那么一切都很好:

If I use pivot_table like below then everything is fine:

test.pivot_table(index = 'A', aggfunc = {'B': 'mean'}, margins = True)

但是，如果我执行以下操作，则无法设置 margins = True(抛出错误 KeyError: 'A'):

However, if I do the following, I can't set margins = True (throws the error KeyError: 'A'):

test.pivot_table(index = test['A'], aggfunc = {'B': 'mean'}, margins = True)

我真的很困惑.假设我需要执行以下操作并且需要设置 margin = True.不可能吗?

I am really confused. Let's say I need do something like below AND need to set margin = True. Is that impossible?

test.pivot_table(index = test['A'].dt.year, aggfunc = {'B': 'mean'}, margins = True)

推荐答案

尝试:

test['Ax']=test['A'].dt.year

test.pivot_table(index = 'Ax' , aggfunc = 'mean', values='B', margins = True)

输出:

        B
Ax
2020  1.5
All   1.5

说明:如果您不传递values，它将默认为df.columns(数据帧的所有列，您'正在旋转).https://github.com/pandas-dev/pandas/blob/v0.25.3/pandas/core/reshape/pivot.py#L87

Explanation: in case if you don't pass values it will default to df.columns (all columns of dataframe, that you're pivoting over). https://github.com/pandas-dev/pandas/blob/v0.25.3/pandas/core/reshape/pivot.py#L87

所以从技术上讲，通过不传递 values，您将所有列传递到 values，但同时仅提供一个函数，所以这就是这个 KeyError 来自.

So technically by passing no values you were passing ALL columns into values, yet at the same time providing function for just one, so this is where this KeyError was coming from.

这里的来源与文档奇怪地不同:https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.pivot_table.html

Source here is oddly off with the documentation: https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.pivot_table.html

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