R help - May 2009 - Problems with sample variance

Dear R users,

I am a beginner to R. I generated 1000 samples with 15 data in each sample

I tried finding the variance for each sample

I used the code:

m=1000;n=15
> r<-rnorm(15000)
> for(i in 1:m){
x=data[,i]
v=var(x)}

what I got was just the variance for the last sample i.e. the 1000th sample

but what I want is 1000 variance.

Does anyone know what I did wrong?

Thanks

Chloe Smith

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Chloe Smith wrote:
> 
> 
> [snip]
> 
> what I got was just the variance for the last sample i.e. the 1000th
> sample
> 
> but what I want is 1000 variance.
> 
> 
m=1000;n=15
r<-matrix(rnorm(m*n),nrow=m)
apply(r,1,var)


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Tena koe Chloe

Try

var(r) 

BTW, it is better to use more than single letters in name your objects
to reduce the chance of conflicting with a standard R object.

HTH ...

Peter Alspach
> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Chloe Smith
> Sent: Thursday, 21 May 2009 12:33 p.m.
> To: r-help at r-project.org
> Subject: [R] Problems with sample variance
> 
> 
> Dear R users,
> 
> I am a beginner to R. I generated 1000 samples with 15 data 
> in each sample
> 
> I tried finding the variance for each sample
> 
> I used the code:
> 
> m=1000;n=15
> > r<-rnorm(15000)
> > for(i in 1:m){
> x=data[,i]
> v=var(x)}
> 
> what I got was just the variance for the last sample i.e. the 
> 1000th sample
> 
> but what I want is 1000 variance.
> 
> Does anyone know what I did wrong?
> 
> Thanks
> 
> Chloe Smith
> 
> --
> View this message in context: 
> http://www.nabble.com/Problems-with-sample-variance-tp23645919
> p23645919.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
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Hi Chloe,

Try this:

NUMBER.OF.RUNS<-10 #change here
for (NR in 1:NUMBER.OF.RUNS)
{
number.simulation<-1000
sample.size=15;
variance.list<-NULL
for(i in 1:number.simulation)
   {
   mysample<-rnorm(sample.size)
   variance.list<- c(variance.list, var(mysample))
   } #i
hist(variance.list)
} #NR


Bests

milton
brazil=toronto

On Wed, May 20, 2009 at 8:16 PM, Chloe Smith <hapiasfion@hotmail.com>
wrote:
>
> Dear R users,
>
> I am a beginner to R. I generated 1000 samples with 15 data in each sample
>
> I tried finding the variance for each sample
>
> I used the code:
>
> m=1000;n=15
> > r<-rnorm(15000)
> > for(i in 1:m){
> x=data[,i]
> v=var(x)}
>
> what I got was just the variance for the last sample i.e. the 1000th sample
>
> but what I want is 1000 variance.
>
> Does anyone know what I did wrong?
>
> Thanks
>
> Chloe Smith
>
> --
> View this message in context:
>
http://www.nabble.com/Problems-with-sample-variance-tp23645919p23645919.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
>
http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>
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