Re: with parallelaxes dumps core

[Philipp K. J. <ja...@ie...>]

On Tue, 27 Jan 2015 03:06:16 -0600
Daniel J Sebald <dan...@ie...> wrote:

> On 01/26/2015 10:38 PM, sfeam wrote:
> > On Monday, 26 January 2015 07:28:19 PM Philipp K. Janert wrote:
> >>
> >> The new plot style "with parallelaxes"
> >> is cute. Unfortunately, it also dumps
> >> core - whenever there are more than 7
> >> columns to plot.
> >
> > The maximum is set at compile time, but
> > yes the default is 7.
> >

Daniel -

Thanks for looking into this!

One comment, though: before going down this
path (of extending the permissible number of
cols in "using") very far, let's consider 
whether this is the right way to do it.

Already, entering 7 explicit col numbers is a
pain. Entering 35 (or whatever) different ones 
is simply not practical.

Should the whole approach be rethought? Is 
"plot" even the right command? I'd argue (not
having looked at the implementation) that we
should consider "splot", because splot naturally
deals with data on a rectangular grid (matrix data).
And that's exactly the type of data used for 
parallel axes plots. Put another way: splot 
already handles dynamic rows AND columns. 

I'll toss in one more thought: whatever solution
is devised, it must contain decent support for
highlighting of individual records and groups of
records. Parallel axes are simply not useful without 
that - and an implementation that does not support 
this action is little more than a demo.

Best,

		Ph.


> 
> Here's the hunk of code from datafile.c that you are referring to:
> 
> 	    /* check we have room for at least 7 columns */
> 	    if (df_max_cols < 7)
> 		expand_df_column(7);
> 
> 	    df_no_cols = sscanf(line, df_format,
> 				&df_column[0].datum,
> 				&df_column[1].datum,
> 				&df_column[2].datum,
> 				&df_column[3].datum,
> 				&df_column[4].datum,
> 				&df_column[5].datum,
> 				&df_column[6].datum);
> 
> and I'm trying to recall how the internal storage of data points
> works. If I'm remembering correctly, there is some type of limitation
> on the number of elements of a data point, e.g., x, y, x tolerance, y 
> tolerance, z (or color), etc. owing to the use of a structure to
> store the data.  Was the size of the structure up to seven elements,
> therefore it was generally thought that only up to seven columns of a
> data file line would be used?  Is this parallel axes plot using the
> same limitation?
> 
> I'm for allowing more than seven columns (note a recursive use of
> sscanf seems required), but at the same time internal memory storage
> should be adjustable too--a much bigger project.  That is, for large
> data sets like images, having seven elements for each point could use
> a lot more memory than necessary.
> 
> Dan
> 
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