# Re: [R] Sorting values within a raster

From: Sara Maxwell <smaxwell_at_ucsc.edu>
Date: Thu, 21 Apr 2011 18:33:22 -0700

Many many thanks,
Sara

Sara M. Maxwell, Ph.D.

On Apr 21, 2011, at 1:26 PM, David Winsemius wrote:

>
> On Apr 21, 2011, at 3:23 PM, Sara Maxwell wrote:
>
>> I am working with a raster and want to take values assigned to each
>> cell and sort them from largest to smallest, then cummulatively sum
>> them together (in order from largest to smallest). I'll then be
>> coding the individual cells such that the top 10% of the largest
>> cell values can be visualize with one color, the next 10% with
>> another and so on.
>>
>> I have tried a number of schemes but am having trouble figuring out
>> how to chose the maximum value, code it and re-search the raster
>> for the next highest value without replacement. I am assuming this
>> requires a loop, unless there is a function that will do this
>> automatically.
>
> ?quantile
>
>>
>> Here is a sample dataset:
>>
>> library(raster)
>> r <- raster(ncol=10, nrow=10)
>> values(r) <- runif(ncell(r))
>
>
> > quantile(values(r), prob=seq(0,1,by=0.1))
> 0% 10% 20% 30% 40%
> 0.004888148 0.106378528 0.217009097 0.307201289 0.364990984
> 50% 60% 70% 80% 90%
> 0.512523817 0.593382875 0.667916094 0.722919876 0.835839832
> 100%
> 0.996683575
>
> You will also need findInterval()
>
> If you want to create a factor that will assign your colors. perhaps
> this could be used to index a suitable color vector:
>
> fac <- findInterval(values(r), quantile(values(r),
> prob=seq(0,1,by=0.1)) )
> > fac
> [1] 6 10 1 10 7 7 8 10 2 9 9 1 6 2 9 1 9 4 2 2
> [21] 3 4 8 9 7 1 9 2 10 5 4 9 8 1 8 10 1 11 3 5
> [41] 5 6 6 5 6 7 4 7 5 3 8 6 3 4 10 4 7 7 8 9
> [61] 10 4 1 8 8 8 3 7 5 1 9 5 2 7 2 10 3 8 4 9
> [81] 6 6 2 6 10 5 5 4 3 6 2 2 1 3 3 3 4 7 1 5
>
> David Winsemius, MD
> West Hartford, CT
>

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