Head or Tails game

Hi,

system.time({
set.seed(111)
colSums(matrix(sample(c(-1, 1), 40*10000, TRUE), ncol = 10000))
})
user? system elapsed 
? 0.032?? 0.012?? 0.041?

system.time({
?set.seed(112)
?list1<-vector("list",10000)
?for(i in 1:10000){
? list1[[i]]<-sample(c(-1,1),40,replace=TRUE)}
? dat1<-do.call(rbind,lapply(list1,function(x) sum(x)))
?dat2<-matrix(dat1,ncol=200,byrow=TRUE)
?})
?? user? system elapsed 
? 0.112?? 0.000?? 0.111?
#modified version

system.time({
?set.seed(112)
?list1<-vector("list",10000)
?for(i in 1:10000){
? list1[[i]]<-sample(c(-1,1),40,replace=TRUE)}
? dat1<-unlist(lapply(list1,function(x) sum(x)))
? })
?user? system elapsed 
?0.092?? 0.000?? 0.092 


It seems like Michael's solution is better in terms of the CPU utilization.? I guess, the loop created the difference.

A.K.



----- Original Message -----
From: Michael Weylandt <michael.weylandt at gmail.com>
To: darnold <dwarnold45 at suddenlink.net>
Cc: "r-help at r-project.org" <r-help at r-project.org>
Sent: Friday, August 3, 2012 10:20 PM
Subject: Re: [R] Head or Tails game

David,

set.seed(123)? # always good to make reproducible 
winnings <- sum(sample(c(-1,1), 10000, replace=TRUE)) 

Unfortunately, that's not the game. The game requires 40 flips of a coin.

Then you have to play the game 10,000 times.

colSums(matrix(sample(c(-1, 1), 40*10000, TRUE), ncol = 10000))

or some such

Michael

D.



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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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