skip()

skip (expr, skipi, skipj)

Sets alternating values of expr to the missing data value.

expr     A valid grid expression that may have 1 or 2 varying dimensions
skipi    Skip factor in the I dimension of expr
skipj    Skip factor in the J dimension of expr

Usage Notes

1. This function is often used while displaying wind arrows or barbs to thin the number of arrows or barbs. It is not necessary to use the skip function on both the U and V wind components; it is sufficient to populate only one component with missing data values to suppress the plotting of the wind arrow or barb.

Examples

1. Suppose you have a time series of 3-hourly data, but you want to display values at 6-hourly time steps:
   
   
   set x 1
set y 1
set t 1 last
d skip(var,2)
   
   
   
2. To display every other grid point in both the X and Y direction:
   
   
   d skip(u,2,2);v
   
   
3. To display every grid point in the Y direction, but every 5th grid point in the X direction:
   
   
   d skip(u,5,1);v
   
   
4. This example script "d_uv.gs" written by Wesley Ebisuzaki automatically sets the skip factor based on the plot dimensions.
   

   *
   * This function does a d skip(ugrd,n);v
   * where n is automatically set to an appropriate value
   *
   * usage: d_uv ugrd vgrd 
   *
   * v1.1 w. ebisuzaki
   * v1.2 4/6/98 revised empirical formula for skip
   *
   function duv(arg)
   u = subwrd(arg,1)
   v = subwrd(arg,2)
   
   * get lat/lon info
   'query dims'
   lons = sublin(result,2)
   lats = sublin(result,3)
   dx = subwrd(lons,13) - subwrd(lons,11)
   dy = subwrd(lats,13) - subwrd(lats,11)
   
   * Determine skip factor 
   dn = dx
   if (dy > dx) ; dn = dy ; endif
   skip = dn / 50 + 0.5
   if (skip < 1) ; skip=1 ; endif
   
   * Display the plot
   'd skip('u','skip');'v