# Substitute raster stack values based on matrix index

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## Substitute raster stack values based on matrix index

 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         [[alternative HTML version deleted]] _______________________________________________ R-sig-Geo mailing list [hidden email] https://stat.ethz.ch/mailman/listinfo/r-sig-geo
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## Re: Substitute raster stack values based on matrix index

 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 <[hidden email]> 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 > > [[alternative HTML version deleted]] > > _______________________________________________ > R-sig-Geo mailing list > [hidden email] > https://stat.ethz.ch/mailman/listinfo/r-sig-geo> Ben Tupper Bigelow Laboratory for Ocean Sciences 60 Bigelow Drive, P.O. Box 380 East Boothbay, Maine 04544 http://www.bigelow.orgTick Forecasting: https://eco.bigelow.org/        [[alternative HTML version deleted]] _______________________________________________ R-sig-Geo mailing list [hidden email] https://stat.ethz.ch/mailman/listinfo/r-sig-geo