#Geoff Williams Purdue University 2020
Note: you have options of how you want to run through the script during the tutorial.
Copy and paste from web page (suggested, but you have to go line-by-line in order, and if you skip/miss a line some of the following lines will not work).
Download the .R file and run the code in basic R (not R Studio) by pressing CTRL-Enter (PCs) or Command-Enter (Macs)
.Rmd file and run the code line-by-line from the script in Rstudio by pressing the Run button . You will have to install and load packages knitr and rmarkdown.
install.packages(c('knitr','rmarkdown'))library(knitr)library(rmarkdown)Today, we are going to learn about how to search the documentation of a package, how to install and load a package, and how to write a function.
Go to the following pages in your web browser, and read the documentation of the package.
https://cran.r-project.org/web/packages/fortunes/fortunes.pdf
You can usually find pages like this by searching google for something like “R package that does X” and one of the first things that comes up will be the pdf documentation for the package. If it doesn’t all you need is the name of the package and you can search for by going here link and clicking on one of the first two links, then press CTRL-F to search or scroll down to find the package.
The first package (cowsay) has several functions in it. The documentation page for every package is organized as follows:
R topics documented is a table of contents with all the functions in the package.
Next, after Index, is a list of the functions with the sections listed in the day one tutorial. I will recap them here for convenience.
Description gives a brief description of what a function does.
Usage provides the syntax. Note that by default, data = NA, nrow = 1, ncol = 1, and byrow = FALSE.
Arguments are the things you put inside the parenteses when you call a function. On the help page, it tells you what you are allowed to pass as input. Note that when you leave out the names of arguments when you are calling the function matrix, R knows what you are telling it to do based on the order of the arguments. If you want to give the arguments of the function out of order, you have to specify their names.
Details tells you additional information you might need to understand what a function is doing.
To install the packages, use the install.packages function. You only have to do this once.
install.packages('cowsay')
install.packages('fortunes')To load a package, use the library function. You have to do this again every time you start R if you want t use functions that are in a package ## Loading packages
library(cowsay)
library(fortunes)Try out some of the functions in cowsay ands fortunes. Personally, I like endless_horse but with endless=FALSE
endless_horse()
endless_horse(endless=F)
say("Oh hay!")By now, you’ve read the documentation for some functions, and you should understand that a function is an object in R that returns output (whatever goes onto the console, or into an object when you put the arrow <- to the left of it) based on the input that you include in the parenteses, separated by commas.
Lets try defining a simple function. First, you put the name you want to give the function, followed by the arrow <- and then function(blah, blahblah) with the arguments in parentheses, separated by commas. This tells R that whenever you use those variables, with those names that you put in the parentheses you use inside the ‘curly brackets’ or ‘curly braces’ { and } to get the from the parentheses when the function is called.
sayhi <- function(name="!") {
print(paste("Hi there ", name))
}Now lets try calling the function. We wrote a function to say hi to the person of your choice.
sayhi(name="Bob.")## [1] "Hi there Bob."sayhi("Bob...")## [1] "Hi there Bob..."sayhi("my friend!")## [1] "Hi there my friend!"sayhi()## [1] "Hi there !"Note that, by default, if you don’t provide an argument to the function, it puts an exclamation point after “Hi” because we specified this in the definition as the default value for the name parameter.
We can write another function that combines cowsay and fortunes. I stole this from https://www.r-bloggers.com/useless-but-fun-r-packages/
animalsayhi <- function() {
animal <- sample(names(animals), 1)
say(paste("Hello, I'm a ", animal, ".", collapse = ""), by = animal)
}
# Now try it out.
animalsayhi()##
## -----
## Hello, I'm a pig .
## ------
## \
## \
## _//| .-~~~-.
## _/oo } }-@
## ('')_ } |
## `--'| { }--{ }
## //_/ /_/ [nosig]
## We can write another fun function, and then we’ll base an excercise off of it. This function takes a name, a verb, a place, and a vehicle. It is called madlib and outputs a madlib.
madlib <- function(name="Mr. Bojangles", verb = "drove", place="town", vehicle="wheelbarrow")
print(paste("The dog ", name, " to ", place, " in a ", vehicle))Try calling the function. Note that you can leave out some arguments, and it uses the default for others, and you can put the arguments in any order you want.
madlib()## [1] "The dog Mr. Bojangles to town in a wheelbarrow"madlib("Jonathan", )## [1] "The dog Jonathan to town in a wheelbarrow"madlib(vehicle="motorcade", name="President Trump")## [1] "The dog President Trump to town in a motorcade"