Imported CSV into R, Missing Values Become "" instead of NA

Question

I tried this command

df<-read.csv("filename.csv",stringsAsFactors=FALSE)

For both, num and int variables, missing values are read as NA. However, for chr, missing values are read as "" instead. When I take the command is.na(""), it returns a FALSE. How do I rectify this?

I tried: str(replace,"",NA"), but it would not work.

Answer 1

Check out ?read.csv, especially the argument na.strings.