Re: multiple plot lines with plot '-'

[Ethan A M. <sf...@us...>]

On Monday, May 14, 2012 10:19:01 am pl...@pi... wrote:
> On 05/14/12 18:27, Ethan A Merritt wrote:
> > The next obvious thought is "can't we remember the values we just read
> > and re-use them if necessary?". But that doesn't work either.
> > Consider:
> >     plot '-' using 1:2, '' using 3:4, '' using 99:100
> > The first plot uses only columns 1 and 2; these values are stored
> > internally and could be used again without rereading.  That's what the
> > "refresh"  command does.  But the 2nd and 3rd plots use data values from
> > columns we didn't use the first time and hence didn't keep.
> > So those values can only be recovered by rereading.
> 
> Since this is all in one plot command , couldn't the whole line be 
> parsed to find all the columns to be required by all the using clauses?
> 
> In fact isn't this already done? Are you implying that
>  
>   plot datafile using 1:2, '' using 3:4, '' using 99:100
> 
> actually reads the data file three times looking at different columns :?

Yes. 

The internal structures that hold data reserve 7 slots for each input
data point.  These 7 slots are just barely enough to hold 
x/y/width/xerr/yerr/color/pointsize/etc of the various plot modes.
There is no mechanism or structure to store an arbitrary number of
additional raw data columns for each line of input.

	Ethan