Looping through a column in R

Question

I am using the R's stats package and would like to loop through column[x] in all the rows of a dataframe, operate on the data in each cell in the column with a function and pass the result to a new column (with the calculated result in the new column aligned with the data in column[x])

I've got two problems:

1. I can't get it to work
2. looping seems to be discouraged in the R articles I've read. Is there an alternative approach and if not, does anyone have an example of how to carry out the loop?

Answer 1

Without any examples, it's hard to know how to respond. The basic case of what you're describing, however, is this:

#Just a very simple data frame
dat <- data.frame(x = c(1, 2, 3))
#Compute the squared value of each value in x
dat$y <- dat$x^2
#See the resultant data.frame, now with column y
dat

When you tell R to square a vector (or vector-like structure, like dat$x), it knows to square each value separately. You don't need to explicitly loop over those values most of the time - although, as Dirk notes, you should only worry about optimizing your loops if they are causing you problems. That said, I certainly prefer reading and writing

dat$y <- dat$x^2

to:

for(i in 1:length(dat$x)){
  dat$y[i] <- dat$x[i]^2
}

... where possible.