你能解释一下这是怎么回事吗？

Question

df = df.loc[-df['Retention time (min)'] < 0]

这是否意味着它正在删除保留时间小于0的行。

Answer 1

它被称为boolean indexing。

只需按条件过滤数据行，此处：

-df['Retention time (min)'] < 0

loc没有必要：

df = df[-df['Retention time (min)'] < 0]

但是如果需要过滤器，还需要一些列loc：

df = df.loc[-df['Retention time (min)'] < 0, 'col1']

样品：

df = pd.DataFrame({'Retention time (min)':[-1,2,3,-6,4,5],
                   'b':[4,5,4,5,5,4]})

print (df)
   Retention time (min)  b
0                    -1  4
1                     2  5
2                     3  4
3                    -6  5
4                     4  5
5                     5  4

df1 = df[-df['Retention time (min)'] < 0]
print (df1)
   Retention time (min)  b
1                     2  5
2                     3  4
4                     4  5
5                     5  4

df2 = df.loc[-df['Retention time (min)'] < 0, 'b']
print (df2)
1    5
2    4
4    5
5    4
Name: b, dtype: int64

与以下内容相同：

df1 = df[df['Retention time (min)'] > 0]
print (df1)
   Retention time (min)  b
1                     2  5
2                     3  4
4                     4  5
5                     5  4

df2 = df.loc[df['Retention time (min)'] > 0, 'b']
print (df2)
1    5
2    4
4    5
5    4
Name: b, dtype: int64