(This article was first published on

**Rcpp Gallery**, and kindly contributed to R-bloggers)The R functions `head`

and `tail`

return the first (last) n elements of the input vector. With Rcpp sugar, the functions `head`

and `tail`

work the same way as they do in R.

Here we use `std::sort`

from the STL and then `tail`

to return the top n items (items with the highest values) of the input vector.

```
#include <Rcpp.h>
using namespace Rcpp;
// [[Rcpp::export]]
NumericVector top_n(NumericVector y, int n){
NumericVector x = clone(y);
std::sort(x.begin(), x.end()); // sort x in ascending order
return tail(x, n);
}
```

A simple illustration:

```
set.seed(42)
x <- rnorm(10)
x
```

[1] 1.37096 -0.56470 0.36313 0.63286 0.40427 -0.10612 1.51152 [8] -0.09466 2.01842 -0.06271

```
top_n(x, 3)
```

[1] 1.371 1.512 2.018

Here we use `std::sort`

from the STL and then `head`

to return the bottom n items (items with the lowest values) of the input vector.

```
// [[Rcpp::export]]
NumericVector bottom_n(NumericVector y, int n){
NumericVector x = clone(y);
std::sort(x.begin(), x.end()); // sort x in ascending order
return head(x, n);
}
```

```
bottom_n(x, 3)
```

[1] -0.56470 -0.10612 -0.09466

To

**leave a comment**for the author, please follow the link and comment on their blog:**Rcpp Gallery**.R-bloggers.com offers

**daily e-mail updates**about R news and tutorials on topics such as: Data science, Big Data, R jobs, visualization (ggplot2, Boxplots, maps, animation), programming (RStudio, Sweave, LaTeX, SQL, Eclipse, git, hadoop, Web Scraping) statistics (regression, PCA, time series, trading) and more...