[R] all combinations with replacement not ordered

[Bert Gunter]

... and actually, since u can be assumed to be of the form shown,

v <-do.call(expand.grid, split(rep(u,len),rep(u,e=len)))


should do.

-- Bert

On Thu, Nov 7, 2013 at 10:06 AM, Bert Gunter <bgunter at gene.com> wrote:
> Well, you can create the expand.grid data frame programmatically via:
>
> u <- 1:3
> len <- length(u)
> v <-do.call(expand.grid, split(rep(u,len),rep(seq_len(len),e=len)))
>
> And then you can use unique.array to get the unique rows after the sort:
>
> unique(t(apply(v,1,sort)))
>
> However, I agree with your sentiments. Not only does this seem
> inelegant, but it will not scale well.
>
> I would imagine a recursive approach would be more efficient -- as
> then only the sets you need would be produced and there'd be no
> sorting, etc. -- but I have neither the time nor interest to work it
> out.
>
> ... and I bet someone already has done this in some R package anyway.
>
> Cheers,
> Bert
>
> On Thu, Nov 7, 2013 at 9:04 AM, Ted Harding <Ted.Harding at wlandres.net> wrote:
>> On 07-Nov-2013 13:38:29 Konstantin Tretiakov wrote:
>>> Hello!
>>>
>>> I need to obtain all possible combinations with replacement when
>>> order is not important.
>>> E.g. I have a population x{1,2,3}.
>>> So I can get (choose(3+3-1,3)=) 10 combinations from this population
>>> with 'size=3'.
>>> How can I get a list of all that combinations?
>>>
>>> I have tried 'expand.grid()' and managed to get only samples where
>>> order is important.
>>> 'combn()' gave me samples without replacement.
>>>
>>> Best regards,
>>> Konstantin Tretyakov.
>>
>> >From your description I infer that, from {1,2,3}, you want the result:
>>
>>   1 1 1
>>   1 1 2
>>   1 1 3
>>   1 2 2
>>   1 2 3
>>   1 3 3
>>   2 2 2
>>   2 2 3
>>   2 3 3
>>   3 3 3
>>
>> The following will do that:
>>
>> u <- c(1,2,3)
>> unique(t(unique(apply(expand.grid(u,u,u),1,sort),margin=1)))
>>
>> #      [,1] [,2] [,3]
>> # [1,]    1    1    1
>> # [2,]    1    1    2
>> # [3,]    1    1    3
>> # [4,]    1    2    2
>> # [5,]    1    2    3
>> # [6,]    1    3    3
>> # [7,]    2    2    2
>> # [9,]    2    3    3
>> #[10,]    3    3    3
>>
>> There may be a simpler way!
>> Ted.
>>
>> -------------------------------------------------
>> E-Mail: (Ted Harding) <Ted.Harding at wlandres.net>
>> Date: 07-Nov-2013  Time: 17:04:50
>> This message was sent by XFMail
>>
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>> and provide commented, minimal, self-contained, reproducible code.
>
>
>
> --
>
> Bert Gunter
> Genentech Nonclinical Biostatistics
>
> (650) 467-7374



-- 

Bert Gunter
Genentech Nonclinical Biostatistics

(650) 467-7374