[R] r-ish ? how can i improve my code?

[Philipp Pagel]

On Wed, Oct 15, 2003 at 10:06:36AM +0100, Sean O'Riordain wrote:


> n <- 900; # number of valid items required...
> 
> x <- numeric(n);
> y <- numeric(n);
> z <- numeric(n);
> 
> c <- 1;  # current 'array' pointer
> tc <- 0; # total items actually looked at...
> 
> while (c <= n) {
>     x[c] = runif(1, 0, 1);
>     y[c] = runif(1, 0, 1);
> 
>     z[c] = sqrt(x[c]^2 + y[c]^2);
>     if (z[c] < 1)
>         c <- c + 1;
>     tc <- tc + 1;
> }
> 
> print("'overwork' ratio");
> print(tc/(c-1));
> plot(x,y);


If I read this correctly you want to find the frequency of the event
"sqrt(x^2 + y^2) < 1" where 0 <= x, y <= 1  
right?

How about this:

n <- 1000
z <- sqrt(runif(n,0,1)^2 + runif(n,0,1)^2)
ratio <- (length(z)-1) / (length( z[z<1] ))

The main difference of course is that I uses a fixed number of "total
items" rather than "valid items". If that's a problem and you need
exactly 900 "valid items" things get a bit more complicated...

cu
	Philipp

-- 
Dr. Philipp Pagel                                Tel.  +49-89-3187-3675
Institute for Bioinformatics / MIPS              Fax.  +49-89-3187-3585
GSF - National Research Center for Environment and Health
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