[R-sig-eco] progamming functions help

[Clément Calenge]

Stephen Cole wrote:
> Not sure if i should really post this here, but i am an ecology
> student and my project is certainly ecological so........
>
> my goal is to use R to write functions for and automate a series of
> analyses i would like to do on a large data set.  The calculations are
> not very difficult in themselves, however they will be very time
> consuming (Plus I think R will be extremely useful and this is another
> excuse to learn how to program).
>
> 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
>
> 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?
>   


x <- c(20,18, 45, 16, 47, 47, 15, 26, 14,14,12,16,35,27,18,94,16,26,
26,30)

matrix(sample(x), ncol=2)


> 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 i will
> need a for loop here but I am unsure of how to do the programing.  I
> am reading two books on S and s-plus now and hope they are some help.
> I thought i would also post on this list and get some expert advice
> for the more experienced R users
>   

## All possible pairs
uu <- expand.grid(x,x)

## the variance on two values? are you sure?
## technically:
apply(uu, 1, var) 


HTH

Clément

> Thank-you very much
>
> Stephen Cole
> Marine Ecology Lab
> Saint Francis Xavier University
>
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>
>   


-- 
Clément CALENGE
Office national de la chasse et de la faune sauvage
Saint Benoist - 78610 Auffargis
tel. (33) 01.30.46.54.14