问题：根据另一个列熊猫数据框提取列值
我有点被困在提取一个变量对另一个变量的条件值上。例如，以下数据框：
A B
p1 1
p1 2
p3 3
p2 4
我如何获得Awhen 的价值B=3？每当我提取的值时A，我都会得到一个对象，而不是字符串。
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
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.
回答 0
您可以loc用来获取满足条件的序列，然后iloc获取第一个元素：
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'
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'
回答 1
您可以尝试query，输入更少：
df.query('B==3')['A']
You can try query, which is less typing:
df.query('B==3')['A']
回答 2
df[df['B']==3]['A']，假设df是您的pandas.DataFrame。
df[df['B']==3]['A'], assuming df is your pandas.DataFrame.
回答 3
使用df[df['B']==3]['A'].values如果你只是想项目本身没有括号
Use df[df['B']==3]['A'].values if you just want item itself without the brackets
回答 4
male_avgtip=(tips_data.loc[tips_data['sex'] == 'Male', 'tip']).mean()
我还为我的任务进行了这种clause和提取操作。
male_avgtip=(tips_data.loc[tips_data['sex'] == 'Male', 'tip']).mean()
I have also worked on this clausing and extraction operations for my assignment.
