通过Pandas中的函数替换NaN时索引超出范围

I have created a function that replaces the NaNs in a Pandas dataframe with the means of the respective columns. I tested the function with a small dataframe and it worked. When I applied it though to a much larger dataframe (30,000 rows, 9 columns) I got the error message: IndexError: index out of boundsI have created a function that replaces the NaN