# Sugar Functions head and tail

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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

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