Question

I have a data frame that’s ~ 50,000 X 200. The column names are 4 different types with numbers on the end ranging from 1-50 (store1, price1, time1, rate1, store2, price2, time2, rate2,…,store50, price50, time50, rate50). I’m trying to create dummy variables depending on the values of each column but am having trouble getting R to handle the column names inside a loop.

store1    price1       time1      rate1     store2     price2    time2     rate2 ....
   A        55.55      08:09      1.44        B         44.44     11:09     1.46
   C        55.55      08:09      1.44        G         44.44     11:09     1.46
   X        55.55      08:09      1.44        E         44.44     11:09     1.46
   D        55.55      08:09      1.44        S         44.44     11:09     1.46

Here’s what I have tried so far with no luck.

xform_data <- function(x) { 
       for(i in 1:50){
       storeX <-  (paste("store",i,sep="")) 
       storeX2  <- ifelse(storeX  == "A", 1, 2)
       x <- cbind(x, storeX2  )
       }
    x    
}

Any suggestions?

Answer 1

The following compares the name instead of the comparing the value:

ifelse(storeX  == "A", ...

Try:

ifelse(x[,storeX]  == "A", ...

Also, all the new columns will be called storeX2. You might prefer to rename them:

x <- cbind(x, storeX2)
colnames(x)[length(colnames(x))] <- storeX2

(I am sure there exist more elegant ways to do it.)