Python 熊猫列值到列？
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Pandas column values to columns?
提问by Idan Gazit
I've seen a few variations on the theme of exploding a column/series into multiple columns of a Pandas dataframe, but I've been trying to do something and not really succeeding with the existing approaches.
我已经看到关于将一个列/系列分解为 Pandas 数据框的多个列的主题的一些变体，但我一直在尝试做一些事情，但并没有真正成功地使用现有的方法。
Given a DataFrame like so:
给定一个像这样的 DataFrame：
key val
id
2 foo oranges
2 bar bananas
2 baz apples
3 foo grapes
3 bar kiwis
I want to convert the items in the keyseries into columns, with the valvalues serving as the values, like so:
我想将key系列中的项目转换为列，并将val值作为值，如下所示：
foo bar baz
id
2 oranges bananas apples
3 grapes kiwis NaN
I feel like this is something that should be relatively straightforward, but I've been bashing my head against this for a few hours now with increasing levels of convolution, and no success.
我觉得这应该是相对简单的事情，但是随着卷积水平的提高，我一直在反对这个问题几个小时，但没有成功。
采纳答案by behzad.nouri
There are a few ways:
有几种方法：
using .pivot_table:
使用.pivot_table：
>>> df.pivot_table(values='val', index=df.index, columns='key', aggfunc='first')
key bar baz foo
id
2 bananas apples oranges
3 kiwis NaN grapes
using .pivot:
使用.pivot：
>>> df.pivot(index=df.index, columns='key')['val']
key bar baz foo
id
2 bananas apples oranges
3 kiwis NaN grapes
using .groupbyfollowed by .unstack:
>>> df.reset_index().groupby(['id', 'key'])['val'].aggregate('first').unstack()
key bar baz foo
id
2 bananas apples oranges
3 kiwis NaN grapes
回答by Zero
You could use set_indexand unstack
你可以使用set_index和unstack
In [1923]: df.set_index([df.index, 'key'])['val'].unstack()
Out[1923]:
key bar baz foo
id
2 bananas apples oranges
3 kiwis None grapes
Or, a simplified groupby
或者，一个简化的 groupby
In [1926]: df.groupby([df.index, 'key'])['val'].first().unstack()
Out[1926]:
key bar baz foo
id
2 bananas apples oranges
3 kiwis None grapes
