Pandas根据多个条件过滤行

Question

我使用pandas 0.13.1 Python 2.7：

我在risk列中有一些既不是Small，Medium或High的值。我想删除值不是Small，Medium和High的行。我尝试了以下方法：

df = df[(df.risk == "Small") | (df.risk == "Medium") | (df.risk == "High")]

但是这会返回一个空数据框。如何正确过滤它们？

Answer 1

我想你想要：

df = df[(df.risk.isin(["Small","Medium","High"]))]

示例：

In [5]:
import pandas as pd
df = pd.DataFrame({'risk':['Small','High','Medium','Negligible', 'Very High']})
df

Out[5]:

         risk
0       Small
1        High
2      Medium
3  Negligible
4   Very High

[5 rows x 1 columns]

In [6]:

df[df.risk.isin(['Small','Medium','High'])]

Out[6]:

     risk
0   Small
1    High
2  Medium

[3 rows x 1 columns]

Answer 2

另一种不错的可读方法是：

small_risk = df["risk"] == "Small"
medium_risk = df["risk"] == "Medium"
high_risk = df["risk"] == "High"

然后您可以像这样使用它：

df[small_risk | medium_risk | high_risk]

或

df[small_risk & medium_risk]