GrADS Command: skip

## 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