Re: [R] Random Relabelling

From: kmatthews <kevin-matthews_at_uiowa.edu>
Date: Mon, 25 Apr 2011 07:53:32 -0700 (PDT)

Thanks to everyone... this helps a lot. Just a quick question about etiquette in this forum (as it my first time questioning)... are notes of gratitude usually given in these forums?

On Wed, Apr 20, 2011 at 1:26 PM, jthetzel [via R] < ml-node+3463799-950416470-231689_at_n4.nabble.com> wrote:

> Kevin,
>
> The following follows John's suggestion, but without the loop. It's quick
> for me.
>
> Jeremy
>
>
> Jeremy T. Hetzel
> Boston University
>
>
>
> ## Generate sample data
> n <- 4000
> rep <- 1000
> rate <- rnorm(n, mean = 15, sd = 2) / 100000 # Mortality rates around
> 15/100k
>
> ## Create an empty matrix with appropriate dimensions
> permutations <- matrix(ncol = n, nrow = rep)
>
> ## Use apply() to resample
> permutations <- apply(permutations, 1, function(x)
> {
> sample(rate, size = n, replace = F)
> })
>
> ## Look at the matrix
> dim(permutations)
> head(permutations)
>
> ## Find the column means
> means <- apply(permutations, 1, mean)
> means
>
>
>
>
>
> On Wednesday, April 20, 2011 1:56:35 PM UTC-4, John Kane wrote:
>
> >
> > There is probably a better way to do this but a for loop like this should
>
> > work. You would just need to change the numbers to yours and then add on
> the
> > locations
> > =========================================================
> >
> > scores <- 1:5
> > mydata <- matrix(data=NA, nrow=5, ncol=10)
> >
> > for(i in 1:10) {
> > mydata[,i] <- sample(scores, 5, replace=FALSE)
> > }
> >
> > =========================================================
> > --- On Wed, 4/20/11, Kevin Matthews <[hidden email]<http://user/SendEmail.jtp?type=node&node=3463799&i=0&by-user=t>>
> wrote:
> >
> > From: Kevin Matthews <[hidden email]<http://user/SendEmail.jtp?type=node&node=3463799&i=1&by-user=t>>
>
> > Subject: Re: [R] Random Relabelling
> > To: "John Kane" <[hidden email]<http://user/SendEmail.jtp?type=node&node=3463799&i=2&by-user=t>>
>
> > Cc: [hidden email]<http://user/SendEmail.jtp?type=node&node=3463799&i=3&by-user=t>
> > Received: Wednesday, April 20, 2011, 1:22 PM
> >
> > I have a map of Iowa of with 4000 locations. At each location, I have a
> > cancer mortality rate. I need to test my null hypothesis; that the
> spatial
> > distribution of the mortality rates is random. For this test, I need to
>
> > establish a spatial reference distribution.
> >
> >
> > My reference distribution will be created by some random relabelling
> > algorithm. The 4000 locations would remain fixed, but the observed
> > mortality rates would be randomly redistributed. Then, I want 1000
> > permutations of the same algorithm. For each of those 1000 times, I
> would
> > record the redistributed mortality rate at each location. Then, I would
>
> > calculate the mean of the 1000 points. The result would be a spatial
> > reference distribution with a mean value of the random permutations at
> each
> > of the 4000 locations.
> >
> > Thanks for the response,Kevin
> >
> > On Wed, Apr 20, 2011 at 11:08 AM, John Kane <[hidden email]<http://user/SendEmail.jtp?type=node&node=3463799&i=4&by-user=t>>
> wrote:
> >
> >
> > Can you explain this a bit more. At the moment I don't see what you are
> > trying to achieve. "calculate the mean of the 1000 values at each of
> the
> > 4000 points" does not seem to make sense.
> >
> > --- On Wed, 4/20/11, kmatthews <[hidden email]<http://user/SendEmail.jtp?type=node&node=3463799&i=5&by-user=t>>
> wrote:
> >
> > > From: kmatthews <[hidden email]<http://user/SendEmail.jtp?type=node&node=3463799&i=6&by-user=t>>
>
> >
> > > Subject: [R] Random Relabelling
> >
> > > To: [hidden email]<http://user/SendEmail.jtp?type=node&node=3463799&i=7&by-user=t>
> >
> > > Received: Wednesday, April 20, 2011, 10:04 AM
> >
> > > I have 4000 observations that I need
> >
> > > to randomly relabel 1000 times and then
> >
> > > calculate the mean of the 1000 values at each of the 4000
> >
> > > points. Any ideas
> >
> > > for where to begin?
> >
> > >
> >
> > > Thanks
> >
> > > Kevin
> >
> > >
> >
> >
> > [[alternative HTML version deleted]]
> >
> > ______________________________________________
> > [hidden email]<http://user/SendEmail.jtp?type=node&node=3463799&i=8&by-user=t>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.
> >
> >
> ______________________________________________
> [hidden email]<http://user/SendEmail.jtp?type=node&node=3463799&i=9&by-user=t>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.
> Jeremy T. Hetzel
> Boston University
>
>
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