Re: multiple plot lines with plot '-'

[sfeam (E. Merritt) <eam...@gm...>]

On Thursday, 17 May 2012, pl...@pi... wrote:
> On 05/16/12 23:05, Ethan A Merritt wrote:
> > Clearly there are benefits on both sides, but up until now we have
> > considered it a priority to minimize internal data storage.
> > 
> Hi Ethan,
> 
> I know your comment here was in the context of the matrix discussion, 
> but in relation to what I was suggesting (reading once only) am I 
> correct in thinking that this would not mean increasing storage, merely 
> filling the same storage a bit earlier?

No, that is not correct.  Gnuplot keeps no history of past plots.
All the data structures pertain only to the current plot, where
"plot" means one clause of the plot or splot statement.  
The data for each clause overwrites the data for the previous plot.
Furthermore, the data that is stored internally does not correspond
1-to-1 to columns of the input data file. Instead what is stored is
the result of evaluating each specifier in the "using" option.
So  
   plot data using (sum [i=1:100] column(i))
stores only two values for each point:
   the index (implicit column(0)) is stored as the x coord
   the sum of columns 1 through 100 is stored as the y coord
Two things to note here are that the x coordinate isn't even
in the data file, and even though 100 numbers are read from
each line in order to calculate a sum, none are stored for later
use.

	Ethan 

> With regards to the changes that would be needed to parse all plot using 
> clauses in one hit, could you point me to the code that would be 
> affected so I can get a better idea of what would be involved? 
> Thanks , Peter.