calculating standard deviation of a grid

[Case.Jon]

Dear Gembud,
 
Does anyone know of a way to calculate the standard deviation of a specific grid using GDLIST?  
There is a function to give you the average of a scalar grid over the GAREA, but I don't see a way to specify a GFUNC that can calculate the standard deviation.  
 
Actually, the only missing link I need is to find the number of non-missing grid points in the array.  I haven't identified such a utility though.  
 
Also, I've looked at the GDSTAT program, but that give you statistics at each individual grid point over a range of times, not stats for a while grid.
 
Your feedback is most welcome!
Jonathan

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