topic Re: 'while loop' on rasters in Python Questions

'while loop' on rasters

MattiasVan_Opstal — Mon, 09 Jan 2012 09:37:21 GMT

A beginners question:
I am looking for the right syntax to perform a while loop on a raster "x",
I want to do something like
while cell (in raster x) > 0:
value of cell= value of cell-1

How can I do this? Probably something easy but I can't find it anywhere.

Thank you

Re: 'while loop' on rasters

AlessandroCinnirella — Mon, 09 Jan 2012 12:18:03 GMT

you can do that using MapAlgebra and the Con() statement:

Con(rasterX > 0, rasterX -1, rasterX)

This means :
if the cell of rasterX is > 0, than the value of the cell will be changed to the value -1,
else, the value will remain unchanged.

ciao
AC

Re: 'while loop' on rasters

MattiasVan_Opstal — Mon, 09 Jan 2012 12:54:54 GMT

Oké, but I want this Con() statement to be repeated until every value of the raster has reached 0.
Similar to the traditional "while-loop" in python...

Re: 'while loop' on rasters

DanPatterson_Retired — Mon, 09 Jan 2012 13:08:22 GMT

This question is confusing. If the cell values are >0 do you simply want to subtract 1 from each value? If so, then use the raster calculator to subtract 1 from the grid and produce a new grid which will be 1 less than the input grid.

Re: 'while loop' on rasters

MattiasVan_Opstal — Mon, 09 Jan 2012 13:25:54 GMT

Sorry for the confusion, what I want to do is:
"While" (as long as...) the cell values of Ras1>0:
Ras2= do something
Ras3= do something
Ras1= Ras1 - 1

Re: 'while loop' on rasters

AlessandroCinnirella — Mon, 09 Jan 2012 13:33:47 GMT

ok, understood:

allzero = 1
while allzero > 0:
   newraster = Con(rasterX > 0, rasterX -1, rasterX)
   maxcellvalue = getRasterProperties_management(newraster, "MAXIMUM")
   if maxcellvalue <= 0:
       allzero = 0

sorry for the bad syntax and the poorness of the code, keep it as an advice.
should do what you need with the proper adjustments 🙂

ciao
AC

Re: 'while loop' on rasters

MattiasVan_Opstal — Mon, 09 Jan 2012 13:43:58 GMT

thanks! I'll try, looks like it will work.
Thank you!