[R-sig-Geo] Substitute raster stack values based on matrix index

[Ben Tupper]

Hi,

I think you want to reform your lookup table into a 2 column matrix with columns from_value and to_value, and then use raster::reclassify()

The one thing that makes me hesitate is the lookup rule you describe.  If a cell has a value of 20 then assign lut value m[20,1]  So does that mean a cell value of 49 gets assigned  m[40,10] ?  What happens to a cell value of 3?  These is no m[0,3].

Cheers,
Ben 


> On Apr 10, 2018, at 12:45 PM, Thiago V. dos Santos via R-sig-Geo <r-sig-geo at r-project.org> wrote:
> 
> I have a large (7000x7000, 10-layered) raster stack whose values range from 0 to 100.
> 
> I need to modify the raster values using the a "lookup table" consisted of a matrix which is 100 rows long by 10 cols wide, where the number of rows is associated with the 0-100 value range of the raster and the number of columns relates to the number of layers of the raster stack. 
> 
> The following code creates a toy example of my dataset:
> 
> # Create raster stackr <- raster(ncol=50, nrow=50)s <- stack(lapply(1:10, function(x) setValues(r, 1:ncell(r))))
> 
> # Create lookup tablem <- matrix(sample(100, 100*10, TRUE), 100, 10)
> 
> Therefore, I need to loop through each cell of the raster and check its value. For example, if the cell value is `20`, then the new value will be reassigned from the 20th line and 1st column in the matrix.
> 
> And so on for the 2nd raster stack layer and 2nd matrix column. And so on for the remaining raster stack layers and matrix columns.
> 
> Any ideas on how to do that?
> 
> I know this sounds a bit cumbersome, but that's how a few ISRIC-WISE's soil datasets are organized!
> Greetings, -- Thiago V. dos Santos
> Postdoctoral Research FellowDepartment of Climate and Space Science and EngineeringUniversity of Michigan
> 
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Ben Tupper
Bigelow Laboratory for Ocean Sciences
60 Bigelow Drive, P.O. Box 380
East Boothbay, Maine 04544
http://www.bigelow.org

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