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R basics, help, mistakes

Some R code basics

<- is known as an “assignment operator” – it means “Make the object named to the left equal to the output of the code to the right”
& means AND, in Boolean logic
| means OR, in Boolean logic
! means NOT, in Boolean logic
When referring to values entered as text, or to dates, put them in quote marks like this: "United States", or "2016-07-26". Numbers are not quoted
When entering two or more values as a list, combine them using the function c, for combine, with the values separated by commas, for example: c("2017-07-26", "2017-08-04")
As in a spreadsheet, you can specify a range of values with a colon, for example: c(1:10) creates a list of integers (whole numbers) from one to ten.
Some common operators:
- + - add, subtract
- * / multiply, divide
- > < greater than less than
- >= <= greater than or equal to, less than or equal to
- != not equal to
Equal signs can be confusing
- == tests whether the objects on either end are equal. This is often used in filtering data
- = makes an object equal to a value, which is similar to <- but used within a function.
Handling null values:
- Nulls are designated as NA
- is.na(x) looks for nulls within variable x.
- !is.na(x) looks for non-null values within variablex`

Here, is.na() is a function. Functions are followed by parentheses, and act on code/data in the parentheses.

Object and variable names in R should not contain spaces

R Workspace

Your current R working environment
Includes any user-defined objects (e.g. vectors, data frames, functions)

Function	Action
`getwd()`	List current working directory
`setwd("mydirectory")`	Change the current working directory to my directory
`ls()`	List the objects in the current work space
`rm(object)`	Delete object
`save(objectlist, file="myfile)`	Save specific objects to a file
`load("myfile")`	Load a work space into the current session (default = .RData)

Packages

Collections of R functions, data, and compiled code in well-defined format
Massively extend the functionality of R
Thousands of user-written packages on CRAN
- https://cran.r-project.org/web/packages

Mac users may need to alter their security preferences to allow apps authored by non-Apple developers to install. If you notice an error, try to change your system preferences.

Getting Help

Function	Action
`help.start()`	General help
`help("foo")` or `?foo`	Help on function foo (the quotation marks are optional)
`help.search("foo")` or `??foo`	Search the help system for instances of the string foo
`example("foo")`	Examples of function foo (the quotation marks are optional)

Working with Packages

install.packages(“packagename”)
update.packages()
library(packagename)
help(package=“packagename”)
library() #what packages are in the library
search() #what packages are loaded

Common Mistakes

Using the wrong case
- help(), Help(), and HELP() are three different functions (and only the first one will work)
Forgetting to use quotation marks when they are needed
- install.packages(“gclus”) will work, while install.packages(gclus) will generate an error.
Forgetting to include the parentheses in a function call
- help() rather than help. Even if there are no options, you still need the().
Using the \ in a path name on Windows
- R sees the backlash character as an escape character.
- setwd("c:\mydata") will generate an error. Use setwd("c:/mydata") or setwd("c:\\mydata") instead
Using a function from a package that is not loaded
- For example: The function str_trim() is contained in the stringr package.
- If you try to use it before loading the package, you will get an error