# Re: calculating standard deviation of a grid

```On Fri, 2007-06-01 at 12:26 -0400, Case.Jon wrote:
```
```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.
```
Jon,

You can determine the number of non-missing grid points in your sub
```
area using a function like:
```GDPFUN   = ysum(xsum(bool(S)))

The bool(S) function will provide a 1/0 output with 1's at existing
points, so
the column sumation of the individual row sums will produce a grid of
the number of non-missing points at all points. You could further assign
the
value to just the non-missing point locations (but not needed here)
with:

The standard deviation of the grid area could be done in GDPLOT2 similar
to:
GDPFUN =
ysum(xsum(bool(tmpc)))//n!mul(savs(tmpc),n)//sm!mul(savs(expi(tmpc,2)),n)//ss!sqrt(quo(sub(ss,quo(mul(sm,sm),n)),sub(n,1))
(or the individual terms above can be computed in GDDIAG to output with
GDLIST).

Steve Chiswell
Unidata User Support

```
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