Looping through a column and returning value

I want to loop through one of the columns in my data frame and check a condition, then replace 0 or 1. The code is :

for (i in v$R){
     if( is.na(v$R) ==TRUE ){v$V5 = 0}else{v$V5=1}
}

But I get an error. The data frame named 'v' is as follow. The V5 has NA values and I want to replace with 0 if values in R columns are NA, and else replace with 1. How can I do that?

A B R V5
1 2 3 NA
4 5 NA NA