Assign values to existing column in SparkR

[xingye]

I have some questions about assign values to a spark dataframe. I want to 
assign values to an existing column of a spark dataframe but if I assign the 
value directly, I got the following error.df$c_mon<-0Error: class(value) == 
"Column" || is.null(value) is not TRUEIs there a way to solve this?