Re: MISSING and UNDEFINED

[Daniel J S. <dan...@ie...>]

Daniel J Sebald wrote:

> I still am wondering if there is a purpose to having both a datafile 
> missing string and datafile undefined string.  Somehow it seems to me 
> the user could have both such items at the same time and want there to 
> be different behavior based upon type.

As I looked at the right side graphs in the PNGs of a couple emails back, I began to wonder even about the behavior of passing a DF_MISSING point through an action table script.  Why should a point go from type DF_MISSING to DF_UNDEFINED just because it goes through a function first?  I doubt anyone desires or expects that.  I hear the compatibility argument, but sometimes improving what looks to have been consequential behavior is rather tempting.

I propose there should be two types of classification strings

set datafile missing ""
set datafile undefined ""

If the df_readascii() routine finds a missing data string such as "NA", return DF_MISSING.  If it finds an undefined string such as NaN, return DF_UNDEFINED.  If the data point is valid but passed through the using function and then becomes undefined then return, what?, DF_UNDEFINED or DF_BAD?

These definitions all depend on meaningful interpretation on gnuplot's part.  If there are meaningful actions to take based upon whether the data is missing or undefined (and both can be present in the same dataset) then that should be the driving factor.  I can't think of any good examples right now, but somehow I think there is meaningful distinction that there could be missing and undefined data points at the same time.

I think that then there might be good reason to eventually have some options for how to utilize the classification in the plots.  This will sound strange, but maybe there should be a way to configure missing points as undefined OR undefined points as missing (but not interchange both because one could simply redefine to achieve that).  That would be in addition to specifications of how to utilize such points in the graph... well, on second thought, if the two classes can be configure in similar ways there really is no need then to have "treat missing as undefined", etc.

Anyway, my feeling is that the behavior of the data can be made much more useful without too much pain and should be before 4.2.  I can see a missing.dem demo with all kinds of plots illustrating nice handling of missing and undefined data.  I really do think that complaints will be few when changing behavior that looks like it wasn't so much planned as it was simply explained.  Useful, controllable plotting will assuage any complaints.

Dan