R help - Feb 2003 - factorial function

Sorry for the stupid question, but is there the factorial function in
R? I tried to find it using help.search('factorial') but got nothing
appropriate. 
Many thanks, 
-Serge

Hi,

----- Original Message -----
From: "Serge Boiko" <boiko at demogr.mpg.de>
To: <r-help at stat.math.ethz.ch>
Sent: Friday, February 14, 2003 11:36 PM
Subject: [R] factorial function

>
> Sorry for the stupid question, but is there the factorial function in
> R? I tried to find it using help.search('factorial') but got
nothing
> appropriate.

There isn't.

But there are at least four different ways to do this -- from the S
Programming Workshop (by Dr. Ross Ihaka):

  # Iteration
  fac1 <- function(n) {
    ans <- 1
    for(i in seq(n)) ans <- ans * i
    ans
  }

  # Recursion
  fac2 <- function(n)
    if (n <= 0) 1 else n * fac(n - 1)

  # Vectorised
  fac3 <- function(n)
     prod(seq(n))

  # Special Mathematical Function -- Gamma
  fac4 <- function(n)
     gamma(n+1)

Of these Gamma is probably the most efficient.  Note that the above hasn't
got any debugging codes, you probably want to add them.

Cheers,

Kevin

------------------------------------------------
Ko-Kang Kevin Wang
Master of Science (MSc) Student
Department of Statistics
University of Auckland
New Zealand
www.stat.auckland.ac.nz/~kwan022

Dear Serge,

For factorial of x, you can use "gamma(x + 1)". Alternatively, you can
install
the gregmisc package which has a "factorial" function that does that
(if I
recall correctly).

Best,




On Friday 14 February 2003 11:36, Serge Boiko wrote:
> Sorry for the stupid question, but is there the factorial function in
> R? I tried to find it using help.search('factorial') but got
nothing
> appropriate.
> Many thanks,
> -Serge
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> http://www.stat.math.ethz.ch/mailman/listinfo/r-help
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