Apart from numbers, perhaps the most useful named objects in R are

**functions**. Nearly everything useful that you will do in R is carried out using a function, and many are available in R by default. You can use (or "call") a function by typing its name followed by a pair of round brackets. For instance, the start up text mentions the following function, which you might find useful if you want to reference R in published work:###### Input:

```
1 citation()
```

###### Result:

> citation() To cite R in publications use: R Development Core Team (2008). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www.R-project.org. A BibTeX entry for LaTeX users is @Manual{, url = {http://www.R-project.org}, title = {R: A Language and Environment for Statistical Computing}, author = {{R Development Core Team}}, organization = {R Foundation for Statistical Computing}, address = {Vienna, Austria}, year = {2008}, note = {{ISBN} 3-900051-07-0}, } We have invested a lot of time and effort in creating R, please cite it when using it for data analysis. See also ‘citation("pkgname")’ for citing R packages.

Many R functions can produce results which differ depending on

**arguments**that you provide to them. Arguments are placed inside the round brackets, separated by commas. Many functions have one or more*optional*arguments: that is, you can choose whether or not to provide them. An example of this is the`citation()`

function. It can take an optional argument giving the name of an R add-on package. If you do not provide an optional argument, there is usually an assumed default value (in the case of `citation()`

, this default value is `"base"`

, i.e. provide the citation reference for the base package: the package which provides most of the foundations of the R language).
Most arguments to a function are *named*. For example, the first argument of the citation function is named *package*. To provide extra clarity, when using a function you can provide arguments in the longer form *name=value*. Thus

citation("base")

does the same as

citation(package="base")

If a function can take more than one argument, using the long form also allows you to change the order of arguments, as shown in the example code below.

###### Input:

```
1 citation("base") #Does the same as citation(), because the default for the first argument is "base"
2 #Note: quotation marks are needed in this particular case (see discussion below)
3 citation("datasets") #Find the citation for another package (in this case, the result is very similar)
4 sqrt(25) #A different function: "sqrt" takes a single argument, returning its square root.
5 sqrt(25-9) #An argument can contain arithmetic and so forth
6 sqrt(25-9)+100 #The result of a function can be used as part of a further analysis
7 max(-10, 0.2, 4.5) #This function returns the maximum value of all its arguments
8 sqrt(2 * max(-10, 0.2, 4.5)) #You can use results of functions as arguments to other functions
9 x <- sqrt(2 * max(-10, 0.2, 4.5)) + 100 #... and you can store the results of any of these calculations
10 x
11 log(100) #This function returns the logarithm of its first argument
12 log(2.718282) #By default this is the natural logarithm (base "e")
13 log(100, base=10) #But you can change the base of the logarithm using the "base" argument
14 log(100, 10) #This does the same, because "base" is the second argument of the log function
15 log(base=10, 100) #To have the base as the first argument, you have to use the form name=value
```

###### Result:

> citation("base") #Does the same as citation(), because the default for the first argument is "base" To cite R in publications use: R Development Core Team (2008). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www.R-project.org. A BibTeX entry for LaTeX users is @Manual{, title = {R: A Language and Environment for Statistical Computing}, author = {{R Development Core Team}}, organization = {R Foundation for Statistical Computing}, address = {Vienna, Austria}, year = {2008}, note = {{ISBN} 3-900051-07-0}, url = {http://www.R-project.org}, } We have invested a lot of time and effort in creating R, please cite it when using it for data analysis. See also ‘citation("pkgname")’ for citing R packages. > #Note: quotation marks are needed in this particular case (see discussion below) > citation("datasets") #Find the citation for another package (in this case, the result is very similar) The 'datasets' package is part of R. To cite R in publications use: R Development Core Team (2008). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. ISBN 3-900051-07-0, URL http://www.R-project.org. A BibTeX entry for LaTeX users is @Manual{, title = {R: A Language and Environment for Statistical Computing}, author = {{R Development Core Team}}, organization = {R Foundation for Statistical Computing}, address = {Vienna, Austria}, year = {2008}, note = {{ISBN} 3-900051-07-0}, url = {http://www.R-project.org}, } We have invested a lot of time and effort in creating R, please cite it when using it for data analysis. See also ‘citation("pkgname")’ for citing R packages. > sqrt(25) #A different function: "sqrt" takes a single argument, returning its square root. [1] 5 > sqrt(25-9) #An argument can contain arithmetic and so forth [1] 4 > sqrt(25-9)+100 #The result of a function can be used as part of a further analysis [1] 104 > max(-10, 0.2, 4.5) #This function returns the maximum value of all its arguments [1] 4.5 > sqrt(2 * max(-10, 0.2, 4.5)) #You can use results of functions as arguments to other functions [1] 3 > x <- sqrt(2 * max(-10, 0.2, 4.5)) + 100 #... and you can store the results of any of these calculations > x [1] 103 > log(100) #This function returns the logarithm of its first argument [1] 4.60517 > log(2.718282) #By default this is the natural logarithm (base "e") [1] 1 > log(100, base=10) #But you can change the base of the logarithm using the "base" argument [1] 2 > log(100, 10) #This does the same, because "base" is the second argument of the log function [1] 2 > log(base=10, 100) #To have the base as the first argument, you have to use the form name=value [1] 2

Note that when typing normal text (as in the name of a package), it needs to be surrounded by quotation marks^{[1]}, to avoid confusion with the names of objects. In other words, in R

citation

refers to a function, whereas

"citation"

is a "string" of text. This is useful, for example when providing titles for plots, etc.

You will probably find that one of the trickiest aspects of getting to know R is knowing which function to use in a particular situation. Fortunately, R not only provides documentation for all its functions, but also ways of searching through the documentation, as well as other ways of getting help.## NotesEdit

- ↑ you can use either single (') or double (") quotes to delimit text strings, as long as the start and end quotes match