4 Control Structures & Functions

4.1 Learning Objectives

Understand If statements
Understand for & while loops
Create new functions & Install Packages

4.2 Conditional Statements

We can tell our code to perform certain tasks if a certain condition is met.

x <- 5

#If the number is greater than 5, get its square
if (x > 5){
  x^2
} else{
  #If not, multiply it by 2
  x*2
}

## [1] 10

# Can incorporate multiple conditions
x <- 7

if (x > 5 && x < 10){
  #If x is greater than 5 AND is less than 10
  x^2
} else if ( x < 0 || x > 10){
  #If x is less than 0 OR greater than 10
  -x
} else {
  x * 2
}

## [1] 49

4.3 For & While Loops

For loops let you iterate over the elements of a vector

#Iterate from 1 to 10

for (i in 1:10){
  print(i)
}

## [1] 1
## [1] 2
## [1] 3
## [1] 4
## [1] 5
## [1] 6
## [1] 7
## [1] 8
## [1] 9
## [1] 10

#Iterate through strings
x <- c('a','ab','cab','taxi')

for (i in x){
  print(i)
}

## [1] "a"
## [1] "ab"
## [1] "cab"
## [1] "taxi"

While loops let you iterate over a piece of code until a condition is no longer met.

x <- 5
#while x is greater than 0
while (x > 0){
  print(x)
  x <- x -1
}

## [1] 5
## [1] 4
## [1] 3
## [1] 2
## [1] 1

4.4 Functions

Sometimes, we need to repeatedly use a sequence of code. Creating functions helps reduce the amount of clutter in our code.

#Example Function that calculates mean

new_mean <- function(values){
  print(values)
  #return()
  sum(values)/length(values)
}

x <- 1:5

mean(x) == new_mean(x)

## [1] 1 2 3 4 5

## [1] TRUE

4.5 Installing packages

There are multiple sources and ways to do this.

CRAN

install.packages(c("dplyr","ggplot2","gapminder","medicaldata"))

BioConductor

For more details about the project you can visit https://www.bioconductor.org

To install packages from BioConductor you first need to install BioConductor itself.

if (!require("BiocManager", quietly = TRUE))
    install.packages("BiocManager")
BiocManager::install(version = "3.16")

Then you can install any package you want by using the install

BiocManager::install("DESeq2")

GitHub

If you want to install the development version of a package, or you are installing something that is only available on GitHub you can use devtools

devtools::install_github('andreacirilloac/updateR')

library(ggplot2)

4.6 Detour || Seeking help

The ? operator in R allows you to get more information about different functions and objects. This will open up the ‘help’ pane in the bottom right of RStudio which will show the documentation for the function/object. This is a great way to get more information.

Concatenate function

?c()

Print the description of an object

str(iris)

## 'data.frame':    150 obs. of  5 variables:
##  $ Sepal.Length: num  5.1 4.9 4.7 4.6 5 5.4 4.6 5 4.4 4.9 ...
##  $ Sepal.Width : num  3.5 3 3.2 3.1 3.6 3.9 3.4 3.4 2.9 3.1 ...
##  $ Petal.Length: num  1.4 1.4 1.3 1.5 1.4 1.7 1.4 1.5 1.4 1.5 ...
##  $ Petal.Width : num  0.2 0.2 0.2 0.2 0.2 0.4 0.3 0.2 0.2 0.1 ...
##  $ Species     : Factor w/ 3 levels "setosa","versicolor",..: 1 1 1 1 1 1 1 1 1 1 ...

4.7 Exercise

Find the help page for the rnorm function. What does it do? Can you print its description? What does it say?

#Find the help page for rnorm  

#Print the description

Intro to R