Re: with parallelaxes dumps core

[Daniel J S. <dan...@ie...>]

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.
>
>> 1) This limitation is not mentioned in
>> the doc. (As far as I can see.)
>
> I thought it was, but now I can't find it either.
> That is an oversight.
>
>> 2) Dumping core unconditionally is not
>> a good user experience. It would be
>> better to detect and reject the illegal
>> input and warn the user.
>
> Indeed.
>
>> 3) The limitation to 7 cols (which, I
>> suspect, depends on limitations in the
>> way "using" is parsed) puts the entire
>> plot style into question. The whole
>> point of parallelaxes plots (to the
>> degree they HAVE a point) is to deal
>> with high-dim data, easily exceeding 7.
>
> If you have such a use-case, go ahead and file a
> feature request.  It should not be too hard to make
> the axis structures dynamic rather than static.
> The original request for this feature provided examples
> from the literature but none of them had even as many
> as 7 axes in a single plot.  So that seemed
> adequate as a default.  Failing to check for more
> columns of input than expected is purely a bug.

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