先從原dataframe取出一個子dataframe，然後再對其中的元素賦值，例如

s = d[d['col_1'] == 0]
s.loc[:, 'col_2'] = 1

就會出現報錯:
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
解決方法:

1. 使用推薦的 .loc[row_indexer,col_indexer] = value
2. 如果不知道，就先copy，再賦值。

s = d[d['col_1'] == 0].copy()
s.loc[:, 'col_2'] = 1