[R] sample within groups-slight problem

[Duncan Murdoch]

On 11-09-06 8:13 PM, Jack Siegrist wrote:
> I want to sample within groups, and when a group has only one associated
> number to just return that number.
>
> If I use this code:
>
> groups<- c(1, 2, 2, 2, 3)
> numbers<- 1:5
> tapply(numbers, groups, FUN = sample)
>
> I get the following output:
>
>>   groups<- c(1, 2, 2, 2, 3)
>>   numbers<- 1:5
>>   tapply(numbers, groups, FUN = sample)
> $`1`
> [1] 1
>
> $`2`
> [1] 3 2 4
>
> $`3`
> [1] 2 3 5 1 4
>
> Can someone tell me why the $'3' result samples all of the numbers and how
> to prevent it from doing so? I want the output for the $'3' part to just be
> 5 in this example.

Because sample(5) gives a permutation of the numbers 1:5.  See the last 
example in ?sample for a way to avoid this "feature".

Duncan Murdoch

>
> Thanks for your help.
>
>
>> sessionInfo()
> R version 2.11.1 (2010-05-31)
> i386-pc-mingw32
>
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