python - Pandas:从带有字符串标题的列中删除某些值

Question

假设我有以下数据框 df :

        First C        Second C       Third C
0       0.104000       0.864000       -999
1       0.060337       0.812470       -999
2       0.065797       0.819570       0.802607
3       0.064715       0.817212       0.801755

我想删除前两行，因为列 Third C显示两个奇怪的值。

df = df.drop(df[df.('Third C') == -999].index)

这会抛出:

       df = df.drop(df[df.('Third C') == -999].index)
                          ^
SyntaxError: invalid syntax

如果我使用 df.['Third C'] 也会发生同样的事情带方括号。如何执行此操作而不必重命名我的列？

Answer 1

仅使用[]并删除.:

df = df.drop(df[df['Third C'] == -999].index)

但最好使用boolean indexing :

df = df[df['Third C'] != -999]

时间:

drop 解决方案速度较慢，因为它使用 bool 索引 和drop:

In [204]: %timeit (df.drop(df[df['Third C'] == -999].index))
1000 loops, best of 3: 691 µs per loop

In [205]: %timeit (df[df['Third C'] != -999])
1000 loops, best of 3: 359 µs per loop