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))

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

Hi David et al,
Thanks for your help.  I spent the afternoon and thought that would  
work but then I realized it was giving a different answer.

I have counts ('hits') in each grid cell, and have then calculated  
the proportion of the total hits represented in each cell (such that  
the sum of all cells = 1).   I want to take the cell with largest  
proportion, add the next largest proportion to it, etc until I reach  
10% of the TOTAL number of 'hits'.  Quantiles unfortunately are  
created using the total number of CELLS and not the total number of  
HITS, if that makes sense.