##### Statistical Analysis with R For Dummies
Functions built into R. Each one consists of a function name immediately followed by parentheses, such as `c()`, `sum()`, `mean()`, and `var()`. Inside the parentheses are the arguments. In this context, "argument" doesn't mean "disagreement," "confrontation," or anything like that. It's just the math term for whatever a function operates on.

Even if a function takes no arguments, you still include the parentheses.

These four R functions are pretty simple in terms of their arguments and their output. As you work with R, however, you encounter functions that take more than one argument.

R provides a couple of ways for you to deal with multiargument functions. One way is to list the arguments in the order in which they appear in the function's definition. R calls this positional matching.

For example, the function `substr()` takes three arguments. The first is a string of characters like `"abcdefg"`, which R refers to as a character vector. The second argument is a start position within the string (1 is the first position, 2 is the second position, and so on). The third is a stop position within the string (a number greater than or equal to the start position). In fact, if you type substr into the Scripts pane, you see a helpful pop-up message that looks like this:

`substr(x, start, stop)`

`Extract or replace substrings in a character vector`

where x stands for the character vector.

This function returns the substring, which consists of the characters between the start and stop positions.

Here's an example:

`> substr("abcdefg",2,4)`

``` [1] "bcd" ``` What happens if you interchange the 2 and the 4?

```> substr("abcdefg",4,2) ``` ```[1] "" ``` This result is completely understandable: No substring can start at the fourth position and stop at the second position.

But if you name the arguments, it doesn't matter how you order them:

```> substr("abcdefg",stop=4,start=2) ``` ```[1] "bcd" ``` Even this works:

```> substr(stop=4, start=2,"abcdefg") ``` `[1] "bcd"`

So when you use a function, you can place its arguments out of order, if you name them. R calls this keyword matching, which comes in handy when you use an R function that has many arguments. If you can't remember their order, just use their names and the function works.

If you ever need help for a particular function — `substr()`, for example — type ?substr and watch helpful information appear on the Help tab.