[R] Programing and writing function help

[Erin Hodgess]

For all possible pairs, you'll have 20^2 pairs.
This is a way to do it:

expand.grid(x[1:20],x[1:20])

HTH,
Erin


On Wed, Oct 8, 2008 at 4:43 AM, Jim Lemon <jim at bitwrit.com.au> wrote:
> Stephen Cole wrote:
>>
>> ...
>> I have a vector of 20 values
>>
>> x <- c(20,18, 45, 16, 47, 47, 15, 26, 14,14,12,16,35,27,18,94,16,26,26,30)
>>
>> 1.
>> I  want to select random pairs from this data set but do it without
>> replacement exhaustively
>>
>
> matrix(x[sample(1:20,20)],nrow=2)
>
> then step through the columns of the resulting matrix
>>
>> I know i can select random pairs without replacement using
>>
>> sample(N,n,replace=F)
>> However i am wondering if there is any way to get 10 random pairs from
>> this
>> data set without repeating any of the data points
>> that is to say if i got a (20, 94) for one pair, i would like to get 9
>> other
>> pairs from the data without again getting 20 or 94?
>>
>> 2.
>> The second thing i would like to do is be able to select all possible
>> pairs
>> of numbers and calculate each pairs variance.
>
> I think you want to use the combn function, but you are going to get a lot
> of pairs...
>
> Jim
>
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-- 
Erin Hodgess
Associate Professor
Department of Computer and Mathematical Sciences
University of Houston - Downtown
mailto: erinm.hodgess at gmail.com