python-3.x - df.where( ) 和 df [ (df [ ] == ) ] 在 Pandas 中的区别，python

Question

任何我可以帮助我说出 Pandas 中这两个语句之间的区别-python

df.where(df['colname'] == value)

和

df[(df['colname'] == value)]

为什么我在输出数据帧中得到不同的大小

Answer 1

根据 where 的文档:

Return an object of same shape as self and whose corresponding entries are from self where cond is True and otherwise are from other.

所以where的目的与使用括号过滤略有不同，因为它会为您提供与您运行它的数据框形状相同的结果。

目标在文档的注释中:

The where method is an application of the if-then idiom. For each element in the calling DataFrame, if cond is True the element is used; otherwise the corresponding element from the DataFrame other is used