python - extract column value based on another column pandas dataframe

Question

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.

Answer 1

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'