# [R] sample within groups-slight problem

Jean-Christophe BOUËTTÉ jcbouette at gmail.com
Wed Sep 7 02:40:16 CEST 2011

2011/9/6 Jean-Christophe BOUËTTÉ <jcbouette at gmail.com>:
you could tapply
function(x) if(length(x)==1) x else sample(x)
or something like this
>
> 2011/9/6 Jean-Christophe BOUËTTÉ <jcbouette at gmail.com>:
>> Hi there,
>> in the third case you get sample(5) which is exactly what you asked for.
>>
>> from ?sample:
>> "If x has length 1, is numeric (in the sense of is.numeric) and x >=
>> 1, sampling via sample takes place from 1:x. Note that this
>> convenience feature may lead to undesired behaviour when x is of
>> varying length in calls such as sample(x). See the examples. "
>>
>> 2011/9/6 Jack Siegrist <jacksie at eden.rutgers.edu>:
>>> 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.
>>>
>>> Thanks for your help.
>>>
>>>
>>>> sessionInfo()
>>> R version 2.11.1 (2010-05-31)
>>> i386-pc-mingw32
>>>
>>> --
>>> View this message in context: http://r.789695.n4.nabble.com/sample-within-groups-slight-problem-tp3794912p3794912.html
>>> Sent from the R help mailing list archive at Nabble.com.
>>>
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>>
>

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