Replace NAs in one variable with values from another variable

Question

How can I replace the \"NAs\" of a variable VAR1 with with the values of the second variable VAR2 to create a third variable VAR3 in R? The data looks like this:

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Answer 1

Here is another approach though I like the transform:

##  dat <- read.table(text="VAR1    VAR2
##   1        NA
##   3        NA
##   NA       1 
##   NA       3
##   2        NA


dat$VAR3 <- dat[, "VAR1"]
dat[is.na(dat[, "VAR3"]), "VAR3"] <- dat[is.na(dat[, "VAR3"]), "VAR2"]
dat
##   VAR1. VAR2. VAR3
## 1     1    NA    1
## 2     3    NA    3
## 3    NA     1    1
## 4    NA     3    3
## 5     2    NA    2
## 6    NA     1    1