[R] Random Relabelling

Jeremy Hetzel jthetzel at gmail.com
Wed Apr 20 20:25:34 CEST 2011

```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)

## 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 <kevin-m... at uiowa.edu> wrote:
>
> From: Kevin Matthews <kevin-m... at uiowa.edu>
> Subject: Re: [R] Random Relabelling
> To: "John Kane" <jrkr... at yahoo.ca>
> Cc: r-h... at r-project.org
> 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 <jrkr... at yahoo.ca> 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 <kevin-m... at uiowa.edu> wrote:
>
> > From: kmatthews <kevin-m... at uiowa.edu>
>
> > Subject: [R] Random Relabelling
>
> > To: r-h... at r-project.org
>
> > 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]]
>
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