基于另一列 pandas 数据框提取列值 [英] extract column value based on another column pandas dataframe

问题描述

我有点卡在从一个变量条件下提取另一个变量的值上.例如，以下数据框:

I am kind of getting stuck on extracting value of one variable conditioning on another variable. For example, the following dataframe:

A  B
p1 1
p1 2
p3 3
p2 4

B=3 时如何获取A 的值?每次我提取A的值时，我得到的是一个对象，而不是一个字符串.

How can I get the value of A when B=3? Every time when I extracted the value of A, I got an object, not a string.

推荐答案

你可以使用 loc 获取满足您条件的系列，然后 iloc 获取第一个元素:

You could use loc to get series which satisfying your condition and then iloc to get first element:

In [2]: df
Out[2]:
    A  B
0  p1  1
1  p1  2
2  p3  3
3  p2  4

In [3]: df.loc[df['B'] == 3, 'A']
Out[3]:
2    p3
Name: A, dtype: object

In [4]: df.loc[df['B'] == 3, 'A'].iloc[0]
Out[4]: 'p3'

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