[R] Finding code for R functions

[Wolfrum, Ed]

Greetings,

I am trying to figure out how to find the source code for R functions. I
am specifically interested in finding the code for the "prcomp"
function. I know that typing the function name without parenthesis will
lead to the code (or to a .Internal or .FORTRAN or .C  call). However, I
don't really understand what is going on. For example, typing "mean"
gives a "UseMethod" response, while typing "mean.default" give the
actual code:

> mean
function (x, ...) 
UseMethod("mean")
<environment: namespace:base>

> mean.default
function (x, trim = 0, na.rm = FALSE, ...) 
---SNIP---
}
<environment: namespace:base>

Why is this? What does "mean.default" mean? I tried the same thing with
"prcomp". With the stats package loaded, I cannot get to the source code
for "prcomp".

> require(stats)
[1] TRUE
> prcomp
function (x, ...) 
UseMethod("prcomp")
<environment: namespace:stats>
> prcomp.default
Error: object "prcomp.default" not found
 
How do I find the prcomp code? Are there general rules for finding the
source code for functions that I should know?

Thanks in Advance,

Edward J. Wolfrum, Ph.D.
National Renewable Energy Laboratory
Golden, Colorado