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: - I can't get it to work - 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?

Accepted Answer

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.

Looping through a column in R

Solution

Problem