Invalid Factor Level, NA generated R

Question

Sample of the data I am working with below. I already omitted all rows with a "NA" in them.

gss.s[1:5,]
      abany          advfront   arrest
2      YES             Agree       NO
3      YES    Strongly agree       YES
10     YES             Agree       YES
16     YES             Agree       NO
21      NO    Strongly agree       NO

I am trying to replace the "YES" with a 1 in the abany column and "NO" with -1 in abany column. I tried using replace replace(gss.s[,1], "YES", 1) but got the error Invalid Factor Level, NA generated. I read a previous post about this same problem and couldn't figure out how to apply the solution to my problem.

Answer 1

You could use ifelse() on the column, changing all values at once.

gss.s$abany <- ifelse(gss.s$abany == "YES", 1, -1)
gss.s
##    abany       advfront arrest
## 2      1          Agree     NO
## 3      1 Strongly agree    YES
## 10     1          Agree    YES
## 16     1          Agree     NO
## 21    -1 Strongly agree     NO

Answer 2

y <- data.frame ("abany"=c("YES","YES","YES","YES","NO"), 
            "advfront"=c("Agree","Strongly Agree","Agree","Agree","Strongly Agree"),
            "arrest"=c("NO","YES","YES","NO","NO"))

I would try another way: Convert factor column to character

y$abany <- as.character.factor (y$abany)

So now you don't have any problem to change values of the column

y[y$abany=="YES", "abany"] <- 1
y[y$abany=="NO", "abany"] <- -1

Answer 3

You can also create a vector in which you define the changes you would like to make. It is a lot quicker if you have big datasets compared to ifelse statements.

translate <- c(YES=1,NO=-1)
gss.s$abany2 <- translate[as.character(gss.s$abany)] 
gss.s

#   abany       advfront arrest abany2
# 1   YES          Agree     NO      1
# 2   YES Strongly agree    YES      1
# 3   YES          Agree    YES      1
# 4   YES          Agree     NO      1
# 5    NO Strongly agree     NO     -1

You also don't have to struggle with nested ifelse functions if you have multiple changes to make:

translate2 <- c('Strongly agree'=2,Agree=1,Disagree=-1,'Strongly disagree'=-2 )
gss.s$advfront2 <- translate2[as.character(gss.s$advfront)]
gss.s

#   abany       advfront arrest abany2 advfront2
# 1   YES          Agree     NO      1         1
# 2   YES Strongly agree    YES      1         2
# 3   YES          Agree    YES      1         1
# 4   YES          Agree     NO      1         1
# 5    NO Strongly agree     NO     -1         2