[R] exaustive subgrouping or combination

[Peter Dalgaard]

David Duffy wrote:
> On Fri, 29 Jun 2007, Peter Dalgaard wrote:
>
>   
>> David Duffy wrote:
>>     
>>>> Waverley <waverley.paloalto at gmail.com> asked:
>>>>
>>>> Dear Colleagues,
>>>>
>>>> I am looking for a package or previous implemented R to subgroup and
>>>> exaustively divide a vector of squence into 2 groups.
>>>>
>>>> -- 
>>>> Waverley @ Palo Alto
>>>>
>>>>         
>>> Google "[R] Generating all possible partitions" and you will find some R 
>>> code
>>> from 2002 or so.
>>>
>>>
>>>       
>> In 2002 this wasn't already in R. These days, help(combn) is more to the 
>> point:
>>
>> mn <- sort(zapsmall(combn(sleep$extra,10,mean)))
>> plot(unique(mn),table(mn))
>> abline(v=mean(sleep$extra[1:10]))
>>
>>     
>
> As I read it, the original query is about partitioning the set eg
> ((1 2) 3) ((1 3) 2) (1 (2 3)).
>
>   
Yes, and

 > combn(3,2)
     [,1] [,2] [,3]
[1,]    1    1    2
[2,]    2    3    3

gives you the first group of each of the three partitions