# Conditional execution exercises

January 26, 2016
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Want to share your content on R-bloggers? click here if you have a blog, or here if you don't. In the exercises below we cover the basics of conditional execution. In all previous exercises, the solutions required one or more R statements that were all executed consecutively. In this series of exercises we’re going to use the `if`, `else` and `ifelse` functions, to execute only a subset of the R script, depending on one or more conditions. Before proceeding, first read section 9.2.1 of An Introduction to R, and the help pages for the `if` and `ifelse` functions.

Answers to the exercises are available here.

Many of the exercises below could be solved using standard functions, like `max` or `abs`. For the purpose of these exercises, however, avoid these functions and try to solve each problem using conditional execution.

Exercise 1
Create an R script that returns the absolute value of an integer vector `x`.

Exercise 2
Create an R script that calculates the square root of a given integer vector `x` of length one, if the value contained in `x` is negative it should return `NA`.

Exercise 3
Create an R script that returns the maximum value out of the elements of a numeric vector `x` of length 2.

Exercise 4
Create an R script that returns `TRUE` if the elements of a vector `x`, with length 3, are strictly increasing.

Exercise 5
Create an R script that returns the max value of a vector `x` with length 3. Don’t use the aid of an auxiliary variable.

Exercise 6
Create an R script that returns the amount of values that are larger than the mean of a vector. You are allowed to use `mean()`.

Exercise 7
Create an R script that, given a numeric vector `x` with length 3, will print the elements by order from high to low.

Image by Ambigraphe (Own work) [GFDL or CC BY-SA 3.0], via Wikimedia Commons

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