# Rcpp::algorithm

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## Introduction

A while back I saw a post on StackOverflow where the user was trying to use `Rcpp::sugar::sum()`

on an `RcppParallel::RVector`

.
Obviously this doesn’t work and it raised the question “Why doesn’t something more generic exist to provide functions with R
semantics that can be used on arbitrary data structures?” As a result, I set out to create a set of such functions following
the pattern of `std::algorithm`

in `Rcpp::algorithm`

.

## Rcpp::algorithm

Currently `Rcpp::algorithm`

contains only a few simple functions, but if they are found to be useful, more will be added.
Examples of using the currently implemented iterator-based functions are below.

### sum, sum_nona, prod, and prod_nona

### min, max, and mean

### log, exp, and sqrt

## Additional Benefits

Through the coding of these simple “algorithms”, a few needs arose.

First, the ability to deduce the appropriate `C`

numeric type
given an `Rcpp`

iterator was necessary. This gave birth to the `Rcpp::algorithm::helpers::decays_to_ctype`

and
`Rcpp::algorithm::helpers::ctype`

type traits. Given a type, these allow you to determine whether it can be cast to a `C`

numeric
type and which type that would be.

Second, the need arose for more information about `R`

types. This gave birth to the `Rcpp::algorithm::helpers::rtype`

traits. These
are defined as follows:

These additional benefits may actually prove more useful than the algorithms themselves. Only time will tell.

## Wrapping Up

There are now some simple iterator-based algorithms that can be used with any structure that supports iterators. They apply the same semantics
as the analogous `Rcpp::sugar`

functions but give us more flexibility in their usage. If you find these to be useful, feel free to request more.

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