[R] ifelse command

[Paul Hiemstra]

Hi Philip,

Why do you want to use ifelse? It is not an alternative to an if then 
else structure, but a way of iterating over a vector with a statement, 
returning one value it is true, another if false. An example:

x = runif(100)
y = ifelse(x > 0.5, "Larger", "Smaller")
x
y

cheers,
Paul

On 08/18/2010 11:18 AM, Philip Wong wrote:
> hello people,
> I want to make a biased dice using the sample() function and print out the
> results after n number of runs, I've successfully generated the dice using
> the following command:
> mydie2<-function(n=1000,y=NULL,...){
> for(i in 1:n){
> x<-sample(1:6,n,replace=TRUE,prob=c(1,1,2,3,2,1)/10)
> x=runif(n)
> if(x<=1/10){y[i]=1}
> else if(x<=2/10){y[i]=2}
> else if(x<=4/10){y[i]=3}
> else if(x<=7/10){y[i]=4}
> else if(x<=9/10){y[i]=5}
> else{y[i]=6}
> }
> bar<-barplot(table(y))
> table<-table(y)
> return(list(bar,table))
> }
>
> mydie2()
>
>
> but I also want to try to create the same dice stimulation using ifelse()
> statement, but all hell break loose when I attempt to use the command below
> (the barplot only shows the results to be 6), can anyone tell me what went
> wrong please:
> mydie2<-function(n=1000,y=NULL,...){
> for(i in 1:n){
> x<-sample(1:6,n,replace=TRUE,prob=c(1,1,2,3,2,1)/10)
> x=runif(n)
> ifelse((x<=1/10),{y[i]<-1},
> ifelse((x<=2/10),{y[i]<-2},
> ifelse((x<=4/10),{y[i]<-3},
> ifelse((x<=7/10),{y[i]<-4},
> ifelse((x<=9/10),{y[i]<-5},{y[i]<-6})))))
>
> }
> bar<-barplot(table(y))
> table<-table(y)
> return(list(bar,table))
> }
>
>
> mydie2()
>    


-- 
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone:  +3130 253 5773
http://intamap.geo.uu.nl/~paul
http://nl.linkedin.com/pub/paul-hiemstra/20/30b/770