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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