df.where( ) 和 df [ (df [ ] == ) ] 在 Pandas 中的区别，python
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Difference between df.where( ) and df [ (df [ ] == ) ] in pandas , python
提问by D3VLPR
Can Any I help me in telling the difference between these two statements in pandas - python
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)
and
和
df[(df['colname'] == value)]
Why Am I getting different sizes in the output dataframe
为什么我在输出数据框中得到不同的大小
回答by Boud
As per the documentation of where:
根据以下文档where：
Return an object of same shape as self and whose corresponding entries are from self where cond is True and otherwise are from other.
返回一个与 self 形状相同的对象，其对应的条目来自 self ，其中 cond 为 True ，否则来自 other 。
So the purpose of whereis slightly different than filtering with brackets, as it will give you the result with the same shape of the dataframe you run it against.
因此， 的目的where与使用括号过滤略有不同，因为它会为您提供与运行它的数据框形状相同的结果。
The goal is in the notes of the documentation:
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
condisTruethe element is used; otherwise the corresponding element from the DataFrameotheris used
where 方法是 if-then 习语的应用。对于在主叫数据帧的每个元素中，如果
cond是True的元件被使用; 否则other使用DataFrame 中的相应元素
