问题描述
经过一些研究,这是答案:
df.loc[:,'quantity'] *= -1 #seems to prevent SettingWithcopyWarning
解决方法
如何将数据框给定列的每个元素与标量相乘?(我曾尝试过寻找SO,但似乎找不到正确的解决方案)
做类似的事情:
df['quantity'] *= -1 # trying to multiply each row's quantity column with -1
给我警告:
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead
注意:如果可能的话,我不想遍历数据框并执行类似的操作…因为我认为整个列上的任何标准数学运算都应该是可能的,而不必编写循环:
for idx,row in df.iterrows():
df.loc[idx,'quantity'] *= -1
编辑 :
我正在跑步0.16.2
熊猫
完整跟踪:
SettingWithCopyWarning:
A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead
See the the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
self.obj[item] = s