I am kind of getting stuck on extracting value of one variable conditioning on another variable. For example, the following dataframe:
我有点卡在另一个变量上提取一个变量条件的值。例如，以下数据帧：
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.
当B = 3时，如何得到A的值？每当我提取A的值时，我得到一个对象，而不是一个字符串。
3 个解决方案
#1
52
You could use loc to get series which satisfying your condition and then iloc to get first element:
您可以使用loc来获得满足条件的系列，然后使用iloc来获取第一个元素：
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'
#2
10
You can try query, which is less typing:
您可以尝试查询，这样可以减少输入：
df.query('B==3')['A']
#3
7
df[df['B']==3]['A'], assuming df is your pandas.DataFrame.
df [df ['B'] == 3] ['A']，假设df是你的pandas.DataFrame。
#1
52
You could use loc to get series which satisfying your condition and then iloc to get first element:
您可以使用loc来获得满足条件的系列，然后使用iloc来获取第一个元素：
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'
#2
10
You can try query, which is less typing:
您可以尝试查询，这样可以减少输入：
df.query('B==3')['A']
#3
7
df[df['B']==3]['A'], assuming df is your pandas.DataFrame.
df [df ['B'] == 3] ['A']，假设df是你的pandas.DataFrame。