Now that we're more comfortable with variables, it's a good idea to discuss some of the variable naming rules in R.

• A valid variable name consists of letters, numbers and the dot (.) or underline (_) characters. The variable name must start with either a letter or a dot that is not immediately followed by a number. In other words, names such as 55weight and .55weight are not valid, whereas .weight is valid.
• We cannot name a variable with any special keywords like if, then, else, or any others that are reserved by the language as part of its built-in functionality. Thus, something like if <- 5 will give you an error.
• R is case sensitive, so the variables Height and height are not the same!

Variable names should be meaningful. For example, if a variable is used for storing a person's height, you will probably call it height and not h.

Sometimes you will want to have a few words in your variable name. R doesn't have an established naming convention for multiple-word variable names. R programmers use multiple conventions, e.g.: separating the individual words with an underscore (salary_tanya) or dot (salary.tanya), or using camelCase capitalization so the individual words stand out (salaryTanya).

It's important to use a consistent naming convention throughout your code. Choose a naming convention and stick to it. Prominent R users, like Hadley Wickham, recommend using lowercase and separate words with underscores in variable names. That's the convention we'll use in our code.