Random Sample with Unique function

Dear R-users

I have a dataset of 243 lines with replicate information for 20 different individuals (ID). 
I would like to randomly sample this dataset 100 times with a selection of unique IDs in each sample.

First to create a random sample I have;

cc<-read.table(blah.blah.blah)
names(cc)
 [1] "CALL"        "CONTEXT"     "ORDER"       "ID"          "STATUS"     

s1<-cc[sample(1:243,20,replace=TRUE),]

This code samples 20 rows from the dataset but can anyone help me write the code to request unique(ID) in this sample?

Thank you so much for your time and help.

Krystyna Golabek

Thanks Uwe, 

Your strata suggestion works, thank you, but it has created a dataset of random rows but without the data, other columns involved. You see I would further like to use this random sample for a DFA (lda) analysis. Can you suggest how I would use the strata function to sample a subset of the data.frame?

Thanks
Krystyna 

Date: Tue, 28 Apr 2009 14:33:22 +0200
From: ligges at statistik.tu-dortmund.de
To: kagolabek at hotmail.com
CC: r-help at r-project.org
Subject: Re: [R] Random Sample with Unique function

In order to use stratified sampling, either try to implement it yourself 
or use the "sampling" package and its function strata() as in:

s1 <- strata(cc, stratanames="ID", size=rep(1, 20), method="srswr")

then you will get 1 observation for each ID. Note that it is not 
important to use "with replacement" in your case, since you only sample 
1 obervation for each stratum.

Uwe Ligges




Krystyna Golabek wrote:

Dear R-users

I have a dataset of 243 lines with replicate information for 20 different individuals (ID). 
I would like to randomly sample this dataset 100 times with a selection of unique IDs in each sample.

First to create a random sample I have;

cc<-read.table(blah.blah.blah)
names(cc)
 [1] "CALL"        "CONTEXT"     "ORDER"       "ID"          "STATUS"     

s1<-cc[sample(1:243,20,replace=TRUE),]

This code samples 20 rows from the dataset but can anyone help me write the code to request unique(ID) in this sample?

Thank you so much for your time and help.

Krystyna Golabek