[R] random sampling problems?

[Jacques VESLOT]

with replacement or not ?

without replacement:
data1 <- cbind(id=1:9, expand.grid(x=1:3,y=1:3))
merge(data1, sapply(data1[,c("x","y")], sample, 3), all.y=T)

why not:
data1[sample(data1$id, 3),]
-------------------------------------------------------------------
Jacques VESLOT

CNRS UMR 8090
I.B.L (2ème étage)
1 rue du Professeur Calmette
B.P. 245
59019 Lille Cedex

Tel : 33 (0)3.20.87.10.44
Fax : 33 (0)3.20.87.10.31

http://www-good.ibl.fr
-------------------------------------------------------------------


zhijie zhang a écrit :
> Dear friends,
>  suppose my dataset is the following data:
> 
> id<-1:9
> x<-c(1,2,3,1,2,3,1,2,3)
> y<-c(1,1,1,2,2,2,3,3,3)
> data<-data.frame(id,x,y)
> 
>      id  x   y
> 1  1   1   1
> 2  2   2   1
> 3  3   3   1
> 4  4   1   2
> 5  5   2   2
> 6  6   3   2
> 7  7   1   3
> 8  8   2   3
> 9  9   3   3
> i want to do sampling like this:say the sample size is 3.
>  First: random sampling from x;
> Next ,random sampling from y ;and combing sampled x and sampled y;
> Finally, output the samples: id x and y.
> I think i could call it two-dimension sampling.
> Thanks very much!
> 
> 
>