[R] ifelse command

[David Winsemius]

On Aug 18, 2010, at 5:18 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()

When problems are posed with a requirement to use a particular  
function, it makes me think there is a homework assignment underlying  
the request, so I will offer a hint rather than making an effort at a  
solution to your full problem. You can use nested ifelse's:

 > set.seed(123); x=runif(20); y<- vector("numeric", length(x))
 > y <- ifelse( x<=1/10, 1, ifelse( x <= 2/10, 2, ifelse (x <= 3/10 ,  
3, 4)))
 > x; y

  [1] 0.28757752 0.78830514 0.40897692 0.88301740 0.94046728  
0.04555650 0.52810549 0.89241904
  [9] 0.55143501 0.45661474 0.95683335 0.45333416 0.67757064  
0.57263340 0.10292468 0.89982497
[17] 0.24608773 0.04205953 0.32792072 0.95450365
  [1] 3 4 4 4 4 1 4 4 4 4 4 4 4 4 2 4 3 1 4 4


> 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()
> -- 
> View this message in context: http://r.789695.n4.nabble.com/ifelse-command-tp2329538p2329538.html
> Sent from the R help mailing list archive at Nabble.com.
>
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David Winsemius, MD
West Hartford, CT