Random sampling based on the observations

Hello!I am having a problem with Random sampling in R. I have used a syntax:
mydata.sub=sample(mydata,7,replace=FALSE,prob=NULL) which allows me to
choose a random sample based on the variables(correct me if I am wrong!).
Suppose I have 10 variable and if I use the above mentioned command then it
will choose 7 variables out of the 10 randomly. My problem is that I want to
have a random sample which is not based on the variables but on the values
of the variables that is the random sample will be based on the
observations. It will be great if someone can help me out me out with a
proper syntax. Thanks in Advance.

On Tuesday 24 March 2009, you wrote:

Hello!I am having a problem with Random sampling in R. I have used a
syntax: mydata.sub=sample(mydata,7,replace=FALSE,prob=NULL) which allows
me
to choose a random sample based on the variables(correct me if I am
wrong!).

Actually, no.
You are sampling from a vector, and where you're using the sampled values
(on 
the rows or on the variables) is up to you.

Let's say we have a dataset with 100 cases and 10 variables:

Case 1:
mydata.sub <- mydata[ , sample(10, 7)]

This will sample 7 variables out of 10.

Case 2:
mydata.sub <- mydata[sample(100, 10), ]

This will sample 10 cases out of 100.

Suppose I have 10 variable and if I use the above mentioned
command then it will choose 7 variables out of the 10 randomly. My
problem
is that I want to have a random sample which is not based on the
variables
but on the values of the variables that is the random sample will be
based
on the observations. It will be great if someone can help me out me out
with
a proper syntax. Thanks in Advance.

I think you need to read the help for:
?"["

and most probably one of the introductory books for R.
I hope this helps,
Adrian


-- 
Adrian Dusa
Romanian Social Data Archive
1, Schitu Magureanu Bd.
050025 Bucharest sector 5
Romania
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     +40 21 3120210 / int.101
Fax: +40 21 3158391


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