R help - Sep 2009 - The code behind the function

Hi R users,
I have a question. How can I see the code behind the function. For example,
> boxplot
function (x, ...) 
UseMethod("boxplot")
<environment: namespace:graphics>

I really would like to see how people code this. Could someone please show
me how to see the code behind the function?
Many Thanks
Tu


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----------------------------------------------------------
How can I see the code behind the function. For example,
> boxplot
function (x, ...) 
UseMethod("boxplot")
<environment: namespace:graphics>

I really would like to see how people code this.
----------------------------------------------------------

That *is* the code.  "boxplot" is a generic function, which calls
another function based on what class of object you pass to it. You can find out
which classes the boxplot method works on by using
> methods("boxplot") 
[1] boxplot.default  boxplot.formula*

   Non-visible functions are asterisked

Next, try typing 
> boxplot.default
to see the implementation for the default function, and then since
boxplot.formula is hidden, usually

getAnywhere("boxplot.formula") 

will retrieve it.

Section 10.9 of An Introduction to R explains this more:

http://cran.r-project.org/doc/manuals/R-intro.html#Object-orientation

Best Regards,
Erik Iverson

Chunhao Tu wrote:
> 
> Hi R users,
> I have a question. How can I see the code behind the function. For
> example,
> 
>> boxplot
> function (x, ...) 
> UseMethod("boxplot")
> <environment: namespace:graphics>
> 
> I really would like to see how people code this. Could someone please show
> me how to see the code behind the function?
> Many Thanks
> Tu
> 
> 

When you type a function name and see something like:

UseMethod("boxplot")

This means the the function you are inquiring about is a "generic
function"-
that is it examines the class of the object passed to it and then calls a
class function. These class functions, also known as methods, all have the
form:

boxplot.<class-name>

So, a quick way to see which methods may be available is to use the methods
function()
> methods( boxplot )
[1] boxplot.default  boxplot.formula* boxplot.matrix

This shows that there are visible methods for objects of class matrix and
stats and a default method that is used in all other cases. Sometimes there
may be other methods that have been hidden in away in package namespaces
where it is harder to find them as in the case of boxplot.formula.

For visible methods, simply type their name to see their contents. I suspect
you will be most interested in boxplot.default:
> boxplot.default
[output omitted]

For non-visible methods, like boxplot.formula, use the getAnywhere function:
> getAnywhere( 'boxplot.formula' )
[output ommitted]

Hope this helps!

-Charlie

-----
Charlie Sharpsteen
Undergraduate
Environmental Resources Engineering
Humboldt State University
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