Question

I have input data from SQL which has fields that are the string “NULL”, such that

unique(file$x) 

returns

Levels: 1 10 14 8 NULL

I would like any of the results that are “NULL” to become “0” and then to convert using as.numeric().

I have tried:

i <- 1
for(i <= nrow(file) {
    if(file$x[i] == "NULL") {
        file$x[i] <- 0
    }
i <- i + 1
}

However, I get the result now that the NULL has simply turned into and I am still unable to convert it to the number 0.

Answer 1

If you’re reading this in with read.csv, set the option na.strings='NULL'. This will import file$x as numeric, instead of factor, with numeric NAs objects in place of the NULL strings. Then to replace NAs with 0s:

file$x[is.na(file$x)] <- 0