[R] ! arithmetic

Thomas Lumley tlumley at u.washington.edu
Mon Feb 17 19:17:03 CET 2003

On Sat, 15 Feb 2003, Stan Markus wrote:

> Since "!" is a logical operator in R, how does one use it in its
> arithmetic sense, say to calculate x!/y!(N-y)! ?

- You can use gamma(x+1) for factorial, or the factorial() function in the
"gregmisc" package
- More usefully, you can use lgamma(x+1) to compute log factorials and
reduce overflow problems if any of the numbers is large
- It's also worth looking at choose() and lchoose() , which compute the
binomial coefficients and their logarithms.


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