[R] Permutation Distribution

[Jacques VESLOT]

 > data1 <- expand.grid(var1=1:15, var2=1:2)
 > test <- replicate(1000, with(data.frame(var1=data1$var1, var2=sample(data1$var2)), 
diff(tapply(var1, var2, mean))))
 > hist(test)
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Jacques VESLOT

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Jacob van Wyk a écrit :
> Hallo
>  
> Is there an elegant way to do the following:
>  
> Dataset consists of 2 variables: var1: some measurements, and var2: a grouping variable with two values, 1 and 2.
> There are (say) 10 measurements from group 1 and 15 measurements from group 2.
> The idea is to study the permutation distribution of mean(group 1) * mean(group2).
> One way would be to permute 1s and 2s and select the corresponding measurements; calculate the difference in means.
> Redo this 1000 times, say. Etc.
>  
> Any help is much appreciated.
> Thanks
> Jacob
>  
>  
> Jacob L van Wyk
> Department of Statistics
> University of Johannesburg, APK
> P O Box 524
> Auckland Park 2006
> South Africa
> Tel: +27 11 489 3080
> Fax: +27 11 489 2832
>  
>  
> 
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