如何在 Pandas DataFrame 上添加列标签

how to add columns label on a Pandas DataFrame

提问by Stefano Fedele

I can't understand how can I add column names on a pandas dataframe, an easy example will clarify my issue:

我不明白如何在 Pandas 数据框上添加列名，一个简单的例子将阐明我的问题：

dic = {'a': [4, 1, 3, 1], 'b': [4, 2, 1, 4], 'c': [5, 7, 9, 1]}
df = pd.DataFrame(dic)

now if I type df than I get

现在如果我输入 df 比我得到

   a  b  c
0  4  4  5
1  1  2  7
2  3  1  9
3  1  4  1

say now that I generate another dataframe just by summing up the columns on the previous one

现在说我只是通过总结前一列的列来生成另一个数据帧

a = df.sum()

if I type 'a' than I get

如果我输入“a”而不是我得到

a     9
b    11
c    22

That looks like a dataframe without with index and without names on the only column. So I wrote

这看起来像一个没有索引且唯一列上没有名称的数据框。所以我写了

a.columns = ['column']

or

或者

a.columns = ['index', 'column']

and in both cases Python was happy because he didn't provide me any message of errors. But still if I type 'a' I can't see the columns name anywhere. What's wrong here?

在这两种情况下，Python 都很高兴，因为他没有向我提供任何错误消息。但是，如果我输入“a”，我在任何地方都看不到列名。这里有什么问题？

采纳答案by ysearka

The method DataFrame.sum()does an aggregation and therefore returns a Series, not a DataFrame. And a Series has no columns, only an index. If you want to create a DataFrame out of your sum you can change a = df.sum()by:

该方法DataFrame.sum()进行聚合，因此返回 a Series，而不是 a DataFrame。并且一个系列没有列，只有一个索引。如果您想从总和中创建一个 DataFrame，您可以a = df.sum()通过以下方式进行更改：

a = pandas.DataFrame(df.sum(), columns = ['whatever_name_you_want'])