Re: Problem and solution: Patch for new "stats" command

[Ethan M. <merritt@u.washington.edu>]

On Wednesday 11 November 2009, Hans-Bernhard Bröker wrote:
> Ethan Merritt wrote:
> 
> > Of course a string is required.  It is going to become the
> > first N characters of a longer string.  
> 
> Erm, no.  It's going to become the first N characters of a variable name.

You are missing the point that in order for it to be useful in a script,
I have to be able to construct the prefix dynamically, which means 
I need to handle the prefix itself as a variable.  Hence: a string variable.

> > How could it be anything other than a string itself?
> 
> By being a (partial) variable name.  And I don't [think] we ever quote a 
> variable name in gnuplot.

Yep. It's a partial name of something.  In other words, it is a substring
of the full name.  To specify or manipulate this substring, I want to put
it in a string variable.

If these names can not be manipulated as variables, and it does seem that
nasty issues are poking their heads out of holes in the woodwork,  then
I don't see any point to having them.  Just pick a fixed set of names and
be done with it.  But then we'll have to come up with some other mechanism
for dealing with multi-column data files, and so far I haven't heard any
other suggestions.   

I am talking about real-world cases here.  To plot multiple curves from a
data file I need to be able to iterate over the columns in the data file.  
I can provide sample data and the desired output if you like.  

If the stats functionality were embedded in the 'plot' command itself,
then I could intersperse reloading of the stats output values with the
individual clauses of the plot command:
   plot \
	'datafile' stats ($5), '' using ($5/stats_max), \
      'datafile' stats ($6), '' using ($6/stats_max), \
	...

Note that each time "stats_max" is encountered during evaluation of the 
plot command, it has been reloaded with a new value by the preceding
stats clause. That works fine for iteration:

   plot for [i=5:20] 'datafile' stats (column(i)), '' using (column(i)/stats_max)

But if the stats are collected via a separate command then, as I
discovered the hard way, it is very cumbersome to collect them into a single
multi-column plot command.  This is true even aside from the question of
using iteration, which anyhow isn't possible with the prototype stats
implementation.