[R] a quick question about "rbinom"

[Bert Gunter]

David!
...
>
> It means the author either doesn't know the 'sample' function, or wants you
> to understand how to use 'rbinom', or that's just the way she thinks.
>
>>> Could someone help? Thanks so much,
>>>
>>>> X1<-c("A","B")[rbinom(n,1,0.6)+1]
>>>> X2<-c("C","D")[rbinom(n,1,0.1)+1]
>
>
> C.f.
>
> X1<-sample( c("A","B"), n,  prob= c(0.6, 0.4))
> X2<-sample( c("C","D"), n,  prob= c(0.6 ,0.4))
... are wrong for n>1 !
e.g.
> X1<-sample( c("A","B"), 5,  prob= c(0.6, 0.4))
Error in sample(c("A", "B"), 5, prob = c(0.6, 0.4)) :
  cannot take a sample larger than the population when 'replace = FALSE'

## You need to add the replace=TRUE argument
> X1<-sample( c("A","B"), 5,  prob= c(0.6, 0.4),replace=TRUE)
> X1
[1] "A" "A" "B" "A" "B"

Cheers,
Bert





>
>>>
>>> It mean index the vector as 1's and 2's  (1st and 2nd item in list)
>>> rather than 0's and 1's because R indices start at 1, not 0.
>>
>>
> Sorry for the blank message.
> --
>
> David Winsemius, MD
> West Hartford, CT
>
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-- 

Bert Gunter
Genentech Nonclinical Biostatistics

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