[R] a quick question about "rbinom"

[David Winsemius]

On Jan 5, 2012, at 12:56 AM, Bert Gunter wrote:

> 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'

The perils of untested code. Thanks, Bert.

>
> ## 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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>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
>
>
> -- 
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
>
> Internal Contact Info:
> Phone: 467-7374
> Website:
> http://pharmadevelopment.roche.com/index/pdb/pdb-functional-groups/pdb-biostatistics/pdb-ncb-home.htm

David Winsemius, MD
West Hartford, CT