Grid MEAN gives NODATA in some output cells

Use the Grid IF statement inside a DOCELL block to test if each input grid's value is NODATA. If it is, skip that grid when calculating the mean at that cell location. If it is not NODATA, add the value to a running total using the += operator. Also, keep a running total of the number of valid values at that cell location. The list of grids can be accessed using an &DO &LIST directive in an AML. For example:

Code:
/*  USAGE: &RUN AVE 'grid1,grid2,grid3,...'
/*
/*  NOTE: Adjust the precision of scalars to mimic precision of
/*  input data.
/*
/*  Put the input grid list in ' ' quotes.

&args list
sum = scalar(0.00)
count = scalar(0.00)
docell
  sum = scalar(0.00)
  count = scalar(0.00)
  &do var &list [unquote %list%]
    if (^(isnull(%var%)))
      begin
        sum += %var%
        count += 1.00
      end
    endif
  &end
  outgrid = sum / count
end
removescalar sum
removescalar count
&return

Note:
The calculation will only occur in areas where the extents of all input grids overlap.