How do I create (Meta) datapoints which do not log values under certain conditions?

[AldoRamos]

I am creating a few datapoints intended to log only certain values.

For example if x is false, for example, there is no valid data to log, so we'll try again next time y changes but no value now.

Pseudo-code:

if (x === true)
then
z = y;
else
// z does not get a value
end if

I find that when I don't return a value in a Meta datapoint, it gets logged as a zero (0.0). How do I accomplish this?

Aldo

[phildunlap]

There has been a little discussion about making that possible, but currently it is not (to my knowledge). So, to do that, you can either use a scripting data source, or you can cause some errors and they won't produce values in that code path. For instance...

if( a == 1 )
  return 50;
else
  return "No value!";

And you can do the same thing by throwing an error rather than returning the wrong datatype, i.e.

throw "No Value";

In either case you may wish to suppress the events for the point / source.

[AldoRamos]

OK, I'll give that a try. Can you suggest any other approaches for filtering unwanted values?

You mentioned using a scripting data source; how would that be different?

[JoelHaggar]

You could try the Discard Extreme values option on the logging setting and return a high value when you don't want to log any data. So rather than throw no value through 999999 and have the data point set to discard any value over 1000.