> -----Original Message-----
> From: r-help-boun...@r-project.org [mailto:r-help-bounces@r-
> project.org] On Behalf Of darnold
> Sent: Friday, August 03, 2012 9:18 PM
> To: r-help@r-project.org
> Subject: Re: [R] Head or Tails game
>
> Wow! Some great responses!
>
> I am getting some great responses. I've only read David, Michael, and
> Dennis
> thus far, leading me to develop this result before reading further.
>
> lead <- function(x) {
> n <- length(x)
> count <- 0
> if (x[1] >= 0) count <- count + 1
> for (i in 2:n) {
> if (x[i] > 0 || (x[i] == 0 && x[i-1] >= 0 )) {
> count <- count + 1
> }
> }
> count
> }
>
> games <- replicate(10000,sample(c(-1,1),40,replace=TRUE))
>
> games_sum <- apply(games,2,sum)
> plot(table(games_sum))
>
> games_lead <- apply(games,2,cumsum)
> games_lead <- apply(games_lead,2,lead)
> plot(table(games_lead))
>
> Now I am going to read Arun, William, and Jeff's responses and see what
> other ideas are being proposed.
>
> Thanks everyone.
>
> D.
>
Here is another solution that doesn't need to define an additional function
with an explicit loop. It seems to be considerably faster than the approach
presented above.
system.time({
set.seed(123)
games <- matrix(sample(c(-1, 1), 40*10000, TRUE), ncol = 10000)
games_sum <- apply(games,2,cumsum)
games_lead <- colSums((games_sum > 0) | (games_sum==0 & games==-1))
})
user system elapsed
0.08 0.00 0.08
plot(table(games_sum[40,]))
plot(table(games_lead))
Compare this with your solution
system.time({
set.seed(123)
games <- replicate(10000,sample(c(-1,1),40,replace=TRUE))
games_sum <- apply(games,2,sum)
games_lead <- apply(games,2,cumsum)
games_lead <- apply(games_lead,2,lead)
})
user system elapsed
0.95 0.02 0.98
Hope this is helpful,
Dan
Daniel J. Nordlund
Washington State Department of Social and Health Services
Planning, Performance, and Accountability
Research and Data Analysis Division
Olympia, WA 98504-5204
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