4.4 The Basics

4.4.1 R as a calculator

Open RStudio, click on the “Console” pane, type 3 + 3 and press enter. R displays the result of the calculation.

3 + 3

## [1] 6

+ is called an operator. R has the operators you would expect for for basic mathematics: + - * / ^. It also has operators that do more obscure things.

* has higher precedence than +. We can use brackets if necessary ( ). Try 1+2*3 and (1+2)*3.

Spaces can be used to make code easier to read.

We can compare with == < > <= >=. This produces a logical value, TRUE or FALSE. Note the double equals, ==, for equality comparison.

    2 * 2 == 4

## [1] TRUE

4.4.2 Creating Objects

You can create objects (make assignments) in R with the assignment operator <-:

    x <- 3 * 4

All R statements where you create objects, assignment statements, have the same form:

object_name <- value

When reading that code say “object name gets value” in your head.

You will make lots of assignments and <- is a pain to type. Don’t be lazy and use=: it will work, but it will cause confusion later. Instead, use RStudio’s keyboard shortcut: Alt + - (the minus sign).

Notice that RStudio automagically surrounds <- with spaces, which is a good code formatting practice. Code is miserable to read on a good day, so giveyoureyesabreak and use spaces.

Objects vs. Variables
What are known as objects in R are known as variables in many other programming languages. Depending on the context, object and variable can have drastically different meanings. However, in this lesson, the two words are used synonymously. For more information see: https://cran.r-project.org/doc/manuals/r-release/R-lang.html#Objects

4.4.3 Naming Objects

The name for objects must start with a letter, and can only contain letters, numbers, underscores (_)and periods (.). The name of the object should describe what is being assigned so they typically will be multiple words. One convention used is snake_case where lowercase words are separated with _. I prefer camelCase where compound words or phrases are written so that each word or abbreviation in the middle of the phrase begins with a capital letter, with no intervening spaces or punctuation and the first letter is lowercase.

    thisIsCamelCase
    some_use_snake_case
    others.use.periods
    Others_pRefer.to_RENOUNCEconvention

To inspect an object you can type its name into the console

## [1] 12

Make another assignment

    aVeryLongAssignmentNameForAVariable <- 20

To inspect this object, try out RStudio’s completion facility: type “aVery,” press TAB, add characters until you have a unique prefix, then press return.

Assume you made a mistake, aVeryLongAssignmentNameForAVariable should have value 30 not 20. Use another keyboard shortcut to help you fix it. Type aVery then press Cmd/Ctrl + ↑. That will list all the commands you’ve typed that start those letters. Use the arrow keys to navigate, then press enter to retype the command. Change 20 to 30 and rerun.