What went wrong when I'm creating a new variable?

Question

I\'d like to create a new variable based on condition imposed on the original variable. Let\'s say

• the original variable, \"var\", is a vector consisted of a rand

Answer 1

You can do this using either ifelse or which. With ifelse you don't need to create the column of NAs first:

mydata$newvar <- ifelse(mydata$var < 10, mydata$var, NA)

If you have already created the column of NAs, this will work:

mydata$newvar[which(mydata$var < 10)] <- mydata$var[which(mydata$var < 10)]