[R] looping

Bert Gunter gunter.berton at gene.com
Tue Feb 27 02:02:34 CET 2007

You do not say -- and I am unable to divine -- whether you wish to sample
with or without replacement: each time or as a whole.

In general, when you want to do this sort of thing, the fastest way to do it
is just to sample everything you need at once and then form it into a list
or matrix or whatever. For example, for sampling 100 each time with
replacement 200 times:

mySamples <- matrix(sample(yourDatavector, 100*200,replace=FALSE),ncol=200)

will give you a 100 row by 200 column matrix of samples without replacement
from yourDatavector. I hope that you can adapt this to suit your needs.

Bert Gunter
Nonclinical Statistics

-----Original Message-----
From: r-help-bounces at stat.math.ethz.ch
[mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Neil Hepburn
Sent: Monday, February 26, 2007 4:11 PM
To: r-help at stat.math.ethz.ch
Subject: [R] looping


I am looking for some help (probably really basic) with looping. What I want
to do is repeatedly sample observations (about 100 per sample) from a large
dataset (100,000 observations).  I would like the samples labelled sample.1,
sample.2, and so on (or some other suitably simple naming scheme).  To do
this manually I would 

>smp.1 <- sample(100000, 100)
>sample.1 <- dataset[smp.1,]
>smp.2 <- sample(100000, 100)
>sample.2 <- dataset[smp.2,]
>smp.50 <- sample(100000, 100)
>sample.50 <- dataset[smp.50,]

and so on.

I tried the following loop code to generate 100 samples:

>for (i in 1:50){
>+ smp.[i] <- sample(100000, 100)
>+ sample.[i] <- dataset[smp.[i],]}

Unfortunately, that does not work -- specifying the looping variable i in
the way that I have does not work since R uses that to reference places in a
vector (x[i] would be the ith element in the vector x)

Is it possible to assign the value of the looping variable in a name within
the loop structure?

Neil Hepburn

Neil Hepburn, Economics Instructor
Social Sciences Department,
The University of Alberta Augustana Campus
4901 - 46 Avenue 
Camrose, Alberta
T4V 2R3

Phone (780) 697-1588
email nhepburn at augustana.ca

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