**Obtaining R**

R is available for Linux, MacOS, and Windows. Software can be downloaded from The Comprehensive R Archive Network (CRAN).

**Startup**

After R is downloaded and installed, simply find and launch R from your Applications folder.

**R program – Entering Commands**

R is a command line driven program. The user enters commands at the prompt (> by default) and each command is executed one at a time.

**R console – The Workspace**

The workspace is your current R working environment and includes any user-defined objects (vectors, matrices, data frames, lists, functions). At the end of an R session, the user can save an image of the current workspace that is automatically reloaded the next time R is started.

**Graphic User Interfaces**

Aside from the built in R console, RStudio is the most popular R code editor, and it interfaces with R for Windows, MacOS, and Linux platforms.

**Operators in R**

R’s binary and logical operators will look very familiar to programmers. Note that binary operators work on vectors and matrices as well as scalars.

Arithmetic Operators include:

Operator | Description |

+ | Addition |

>- | Subtraction |

* | Multiplication |

/ | Division |

^ or ** | Exponentiation |

**Logical Operators include:**

Operator | Description |

> | greater than |

>= | greater than or equal to |

< | less than |

=< | less than or equal to |

== | exactly equal to |

!= | not equal to |

**Data Types**

R has a wide variety of data types including scalars, vectors (numerical, character, logical), matrices, data frames, and lists.

**Creating New Variables**

Use the assignment operator <- to create new variables.

# An example of computing the mean with variables

mydata$sum <- mydata$x1 + mydata$x2 mydata$mean <- (mydata$x1 + mydata$x2)/2

**Functions**

Almost everything in R is done through functions. A function is a piece of code written to carry out a specified task; it may accept arguments or parameters (or not) and it may return one or more values (or not!). In R, a function is defined with the construct:

function ( arglist ) {body}

The code in between the curly braces is the body of the function. Note that by using built-in functions, the only thing you need to worry about is how to effectively communicate the correct input arguments (arglist) and manage the return value/s (if any).

**Importing Data**

Importing data into R is fairly simple. R offers options to import many file types, from CSVs to databases.

For example, this is how to import a CSV into R.

# first row contains variable names, comma is separator

# assign the variable id to row names

# note the / instead of \ on mswindows systems

mydata <- read.table("c:/mydata.csv", header=TRUE, sep=",", row.names="id")

**Descriptive Statistics**

R provides a wide range of functions for obtaining summary statistics. One way to get descriptive statistics is to use the sapply( ) function with a specified summary statistic.

Below is how to get the mean with the sapply( ) function:

# get means for variables in data frame mydata

# excluding missing values

sapply(mydata, mean, na.rm=TRUE)

Possible functions used in sapply include mean, sd, var, min, max, median, range, and quantile.

**Plotting in R**

In R, graphs are typically created interactively. Here is an example:

# Creating a Graph

attach(mtcars) plot(wt, mpg) abline(lm(mpg~wt)) title("Regression of MPG on Weight")

The plot( ) function opens a graph window and plots weight vs. miles per gallon. The next line of code adds a regression line to this graph. The final line adds a title.

**Packages**

Packages are collections of R functions, data, and compiled code in a well-defined format. The directory where packages are stored is called the library. R comes with a standard set of packages. Others are available for download and installation. Once installed, they have to be loaded into the session to be used.

.libPaths() # get library location library() # see all packages installed search() # see packages currently loaded

**Getting Help**

Once R is installed, there is a comprehensive built-in help system. At the program’s command prompt you can use any of the following:

help.start() # general help help(foo) # help about function foo ?foo # same thing apropos("foo") # list all functions containing string foo example(foo) # show an example of function foo

**Going Further**

If you prefer an online interactive environment to learn R, there are free R tutorials by DataCamp is a great way to get started.

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