R help - Apr 2011 - Sorting values within a raster

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.

Here is a sample dataset:

library(raster)
r <- raster(ncol=10, nrow=10)
values(r) <- runif(ncell(r))

Many thanks for any input,
Sara Maxwell
---------------------------------------------------
Sara M. Maxwell, Ph.D.
UC Santa Cruz

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