setting column of dataframe by index of slice of same dataframe in pandas not working

Question

I'm trying to set values of column for some rows of dataframe based on index of dataframe view. This does not work as expected. What are altrenatives?

i tried following code:

df=pd.DataFrame({'a':[1,2,3]})
dfb=df[df.a>1]
df['c']=np.nan
df.loc[dfb[dfb.a>2].index]['c']=10
df.loc[dfb[dfb.a>2].index]

expected that c column of df.loc[dfb[dfb.a>2].index] would be 10. it is still nan

Answer 1

尝试将df.loc[dfb[dfb.a>2].index]['c']=10更改为df.loc[dfb[dfb.a>2].index,'c']=10 。