LOOP not working in R

Question

This doesn't work and I'm not sure why.

look_up  <- data.frame(flat=c("160","130"),
                   street=c("stamford%20street", "doddington%20grove"),
                   city = c("London", "London"),
                   postcode = c("SE1%20", "se17%20"))

new <- data.frame()
for(i in 1:nrow(look_up)){
  new <- rbind(new,look_up$flat[i])
}

Grateful if someone could tell me why please! My result should be a data frame with one column called 'flat' and the values of 160 and 130 on each row. Once I understand this I can move onto the real thing I'm trying to do!

Answer 1

No need for a loop:

look_up[,"flat",drop=FALSE]

As mentioned, the problem with your loop is automatic conversion to factors. You can put options(stringsAsFactors=FALSE)in front of your script to avoid that.

However, it's almost certain that you are approaching your actual problem in the wrong way. You should probably ask a new question, where you tell us what you actually want to achieve.

Answer 2

You could also do something like:

> look_up  <- data.frame(flat=c("160","130"),
+                        street=c("stamford%20street", "doddington%20grove"),
+                        city = c("London", "London"),
+                        postcode = c("SE1%20", "se17%20"))
> 
> new <- look_up[,1,drop=FALSE]
> new
  flat
1  160
2  130
> class(new)
[1] "data.frame"

This shows your final desired output is a dataframe with 160 and 130 on columns. If you don't include drop=FALSE here, then your final output will be a factor. Hope this helps.

Answer 3

You need to look into the stringsAsFactors argument of data.frame.

look_up  <- data.frame(flat=c("160","130"),
                   street=c("stamford%20street", "doddington%20grove"),
                   city = c("London", "London"),
                   postcode = c("SE1%20", "se17%20"), 
                   stringsAsFactors = FALSE)
look_up[, "flat", drop = FALSE ]