timecolumn()

[Hans-Bernhard B. <br...@ph...>]

Hello, guys.

A while ago, Ethan asked what the secret function timecolumn() was 
about.  Then, more recently, a bug reporter ended up needing it as the 
way to work around a limitation, but it didn't work...  I just patched 
it and added documentation, but some open issues remain.

timecolumn() is sitting between a rock and a hard place because of the
way I implemented multiple separate timefmt specifications a long time 
ago (part of the 'axis patch'), yet another feature that was never 
actually documented.  Each axis can have its own timefmt string.

But parsing of time/date input doesn't really have anything to with axes 
--- it deals with datafile columns.   Taking into account extended using 
specs, the relation between column numbers and axes is many-to-many, so 
the two really have no particular link to each other.

The obviously correct solution would be to pass a timeformat string 
directly as a second argument to timecolumn().  Back when I added 
per-axis timefmt strings, that wasn't possible.  Nowadays, with the 
stringvariables patch integrated, it probably is.

So: anybody interested in implementing support for

	plot 'file' using (timecolumn(1,'%Y-%m-%d %H:%M:%S')):5

or
	tf1='%Y-%m-%d %H:%M:%S'
	plot 'file' using (timecolumn(1,tf1)):5