Using apply in a 'window'

Question

Is there a way to use apply functions on 'windows' or 'ranges'? This example should serve to illustrate: ``` a <- 11:20 ``` Now I want to calculate the sums of consecutive elements. i.e. [11+12, 12+13, 13+14, ...] The ways I can think of handling this are: ``` a <- 11:20 b <- NULL for(i in 1:(length(a)-1)) { b <- c(b, a[i] + a[i+1]) } # b is 23 25 27 29 31 33 35 37 39 ``` or alternatively, ``` d <- sapply( 1:(length(a)-1) , function(i) a[i] + a[i+1] ) # d is 23 25 27 29 31 33 35 37 39 ``` Is there a better way to do this? I'm hoping there's something like: ``` e <- windowapply( a, window=2, function(x) sum(x) ) # fictional function # e should be 23 25 27 29 31 33 35 37 39 ```

Accepted Answer

Here's an anternative using `rollapply` from zoo package

```
> rollapply(a, width=2, FUN=sum )
[1] 23 25 27 29 31 33 35 37 39
```

zoo package also offers `rollsum` function

```
> rollsum(a, 2)
[1] 23 25 27 29 31 33 35 37 39
```

Using apply in a 'window'

Solution

Problem