R help - Aug 2003 - Viewing function source

I know I should probably RTFM for this question, but could someone tell me
if R supports the idea of "viewing source" on any particular function
you
want to use?

If I want to "view source" on the rpois() function, for example, can I
do
somethink like:

source(rpois)

To see how the function is implemented?

Regards,

Paul Meagher

Datavore Productions
50 Wood Grove Drive
Truro, Nova Scotia
B2N-6Y4
1.902.895.9671
www.datavore.com

Paul Meagher wrote:
> If I want to "view source" on the rpois() function, for example,
can I do
> somethink like:
> 
> source(rpois)
> 
> To see how the function is implemented?
> 
  You mean you've never typed 'ls' instead of 'ls()' and
discovered this
for yourself? I still do it all the time, and I've been using S/R for 
ten+ years :)

  Ah, maybe you're not a Unix person ('ls' is the command to list
files).

  Just type a function name to see the source, or to see how it 
disappears into R's internal code. You can also do print(rpois), but 
you'll see for rpois it disappears into internal code:

function (n, lambda)
.Internal(rpois(n, lambda))
<environment: namespace:base>

  - now you need to get the full source code for R and look into C code.

Baz

Most of the time you just use

rpois

or, to use a pager,

page(rpois)

For some functions the function is hidden from the end user, and for those 
(indeed, for any object the system can find) you can use

getAnywhere("foo.bar")


In your example, it will not be too revealing:
> rpois
function (n, lambda)
.Internal(rpois(n, lambda))

....

On Tue, 26 Aug 2003, Paul Meagher wrote:
> I know I should probably RTFM for this question, but could someone tell me
> if R supports the idea of "viewing source" on any particular
function you
> want to use?
> 
> If I want to "view source" on the rpois() function, for example,
can I do
> somethink like:
> 
> source(rpois)
> 
> To see how the function is implemented?

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

> If I want to "view source" on the rpois() function, for example,
can I do
> somethink like:
> 
> source(rpois)
> 
> To see how the function is implemented?
Just type the name of the function

On Tue, 26 Aug 2003, Paul Meagher wrote:
> I know I should probably RTFM for this question, but could someone tell me
> if R supports the idea of "viewing source" on any particular
function you
> want to use?
>
> If I want to "view source" on the rpois() function, for example,
can I do
> somethink like:
>
> source(rpois)
>
> To see how the function is implemented?
It's even simpler in most cases, but you have picked an especially
complicated example


Just type the name of the function to see the R code
  > rpois
  function (n, lambda)
  .Internal(rpois(n, lambda))

But in this case it tells you that rpois is implemented in C code :(

 By convention, it is likely to be a function called do_rpois,
 however in this case we have an exception to the convention.  You can
look in src/main.names.c for the name of the C function.

abacus% fgrep rpois names.c
{"rpois",       do_random1,     3,      11,     2,      {PP_FUNCALL,
PREC_FN,0}},

so the function do_random1 is actually involved. If you grep for that, you
are directed to src/main/random.c and you will eventually find that the
underlying code is in src/nmath/rpois.c and is commented with a reference
to the ACM Transactions on Mathematical Software.


	-thomas