Giving values a name

A result that R only shows is gone the next moment. To keep calculating with it, you give it a name. Programmers call this a variable: a name with a value behind it.

The arrow

With <- you store a value under a name. The arrow reads as "gets": price gets the value 1.09. From then on the name stands for the value, and R shows it as soon as you write it on a line of its own:

price <- 1.09
price_with_tax <- price * 1.07
price_with_tax

The first and second lines show nothing, because assigning is not showing. Only the third asks for the value.

= also works for assignment, but the arrow is customary in R, and that is also how most examples you find online are written.

Overwriting

If you assign a new value to a name, the old one is gone. That also holds when the new value is calculated from the old one:

litres <- 2
litres <- litres + 1
litres

Good names

A name may contain letters, digits, _ and ., but must start with a letter. Spaces are not allowed, and R distinguishes upper and lower case: Price and price are two different names.

It is customary to write names in lower case and separate words with _, such as price_per_litre. A good name says what is in it; x does not.

When R does not know a name

If you make a typo, or use a name before assigning anything to it, R reports that it cannot find the object:

price <- 1.09
prise * 2

You will meet this message often. Almost always it is a typo or a line that has not been run yet.

Key points

• <- gives a value a name that you can use instead of the value.
• A new value overwrites the old one.
• Names in lower case, with _ between words; case matters.