R help - Jul 2007 - looking at a function's code

Good morning,

I'd like to look at the code for the R function head.  When I type just the
word head, I get back

function(x, ...)
UseMethod("head")
<environment: namespace:utils>


I expected to see several lines of R code.  Any suggestions?

Thanks,

Walt Paczkowski

On 16/07/2007 8:02 AM, Walter Paczkowski wrote:
> Good morning,
> 
> I'd like to look at the code for the R function head.  When I type just
the word head, I get back
> 
> function(x, ...)
> UseMethod("head")
> <environment: namespace:utils>
> 
> 
> I expected to see several lines of R code.  Any suggestions?
Even though it's not very informative, that really is the source for 
that function.  For instructions on how to see the more useful stuff, 
see Uwe Ligges' article in the Oct 2006 R News (available at 
http://cran.r-project.org/doc/Rnews/Rnews_2006-4.pdf).

Duncan Murdoch

Walter Paczkowski wrote:
> Good morning,
> 
> I'd like to look at the code for the R function head.  When I type just
the word head, I get back
> 
> function(x, ...)
> UseMethod("head")
> <environment: namespace:utils>
> 
> 
> I expected to see several lines of R code.  Any suggestions?
  Have a look at:

https://svn.r-project.org/R/trunk/src/library/utils/R/head.R

  Also, ?head shows methods for different types of objects, and you can
see these with

getAnywhere(head.default)

or

utils:::head.default
> Thanks,
> 
> Walt Paczkowski
> 
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Walter Paczkowski:
> I'd like to look at the code for the R function head. ?When I type just
> the word head, I get back
> 
> function(x, ...)
> UseMethod("head")
> <environment: namespace:utils>
This basically means that 'head' is a generic function that works in
different ways for different classes of objects (data frames, matrices,
tables &c.) Many function, e.g., 'plot' and 'mean', work the
same way.

Type ?UseMethod for a better/longer explanation.

Now type

methods(head)

You will get:

[1] head.data.frame* head.default*    head.ftable*     head.function*
[5] head.matrix      head.table*

Now, ordinarily you should be able to write 'head.data.frame' to see the
code for this function, but, since it is starred, '*', this doesn't
work.
The easiest way to get hold of it is using 'getAnywhere':

getAnywhere(head.data.frame)

-- 
Karl Ove Hufthammer