Variables and Assignments

The command for assigning a value to a variable is <-. You can basically use any name for a variable, although it will cause problems if you give a variable the same name as a function, so be careful not to use c or length as a variable name. Although innocuous, these are both functions in S-PLUS. If you do accidentally give a variable the same name as a function, remove the variable from your .Data area (see below).

Variable names can be as long as you need, but should not contain blank spaces. If you have two words in a variable name, such as ``Water Depth'', you could write it as WaterDepth, waterdepth, or water.depth. You may not separate words with an underscore (that is a special character in S-PLUS) or a dash (that would be interpreted as a minus sign).

To assign the value 9 to the variable x, type:

> x <- 9

(Read this as ``x gets 9''.) Note that S-PLUS does not return any output after an assignment. If you type the variable name, S-PLUS will return its value (if you are ever unsure, this is a good way to confirm that an assignment was successful).

Now that x has a value, it can be manipulated like any other number.

> sqrt(x)
[1] 3

> y <- (5 * (x + 2)) - 3

These manipulations do not affect the value of x, it is still 9. To change it, you must assign a new value to x.

> sqrt(x)
[1] 3
> x
[1] 9
> x <- sqrt(x)
> x
[1] 3

Text values can also be assigned to a variable:

> y <- "hello"
> y
[1] "hello"

The variables x and y are now stored in your .Data directory. This means you will be able to use them for the remainder of this session and any time you run S-PLUS in the future. For a list of objects in your directory, use the objects() command. Unneeded objects may be removed with the remove or rm commands. The two work the same, only remove requires quotation marks around the argument, for instance remove("x") is the same as rm(x).

Question: How do you exchange the values of x and y?