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 Third C 列显示了两个奇怪的值。

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

抛出:

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

如果我使用带方括号的 df.['Third C'] 也会发生同样的事情。如何在不重命名列的情况下执行此操作？

Answer 1

仅使用 [] 并删除 。:

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

但是最好用boolean indexing :

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

时间:

drop 解决方案较慢，因为它使用了 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