Re: question about binary plot data

[Chris K <gnu...@li...>]

Daniel J Sebald wrote:
> Chris K wrote:
> 
>> outd.data is exactly 10 floats long (40 bytes)
>>
>> cat test-2.gp outd.data out.data | gnuplot  WORKS
>> cat test-3.gp outd.data out.data | gnuplot  WORKS
>> cat test-4.gp outd.data out.data | gnuplot  FAILS
>> cat test-4.gp outd.data out.data outd.data | gnuplot  WORKS
> 
> If you mean that it plots, then yes "WORKS" is correct.  However, I
> think this isn't working the manner you intend.

That's what I meant.

> 
> It's subtle because of the fact the data within the file looks to be a
> simple linear or affine relationship.  Thus, the shape of the curve when
> gnuplot does or doesn't generate the index data is about the same.  Read
> on...

Yup, just 0..9

> 
>>> This works:
>>>
>>> set title "test-2.gp"
>>> plot "-" binary record=10 using 0:1 with linespoints,\
>>>     "-" binary record=10 using 0:($1)**2 with linespoints
> 
> It specifies record of 10 and since "0" is a special qualifier in
> gnuplot meaning to generate the index data 10x1=10 floats for the first
> line and 10*1=10 floats for the second line.  No problem; a plot with
> red and green lines each containing 10 points.  (I'll send you the PNGs
> in a separate email.)
> 

My plots look like your PNGs

> There may be a bug here however.  I notice that with "0" the index
> starts at "-1" on the plot.  That doesn't seem a reasonable place to
> start.  It should be either "0" or "1".  I will check the documentation
> to see if the start value is specified and will fix it accordingly.

Yeah, I did not pay attention to the (-1) starting x-scale.  That is even
weirder than I thought.  Definitely a bug from my POV.

>>>
>>> This works:
>>>
>>> set title "test-3.gp"
>>> plot "-" binary record=10 using 0:1 with linespoints,\
>>>     "-" binary record=5x2 using 1:($2)**2 with linespoints
> 
> Again, there is a "0" on the first line so that is 10x1=10 floats.  But
> now the second line is saying that the record inside the binary file is
> 5 by 2 or five pairs (or five 2 tuples) and the using syntax says to use
> the first coordinate of the pair and the second coordinate of that
> pair.  The "record" and "using" do no conflict, but the specification is
> that there are only 5 points.
> 
> So if you look at the graphs you should see there are only 5 points for
> "test-3.png".  As I said before, because of the linear nature of the
> data, you may have seen the two and thought that "test-2" and "test-3"
> plotted the same but in fact they are different.

I knew they were different.  I was mainly worried about crashing.

> 
>>>
>>> This fails, saying "line 0: warning: Skipping data file with no valid
>>> points"
>>>
>>> set title "test-4.gp"
>>> plot "-" binary record=5x2 using 1:2 with linespoints,\
>>>     "-" binary record=5x2 using 1:($2)**2 with linespoints
>>>
>>> The use of 5x2 instead of 10 in the first plot triggers the error.  I
>>> am going
>>> to hypothesize that the first use of "record=5x2" causes it to read
>>> an amount of
>>> data greater than "record=10".
> 
> You may be correct.  But I don't see why if fails.  This could be a
> strange "loose end" kind of bug (an unaccounted for boundary value or
> something) because the "record" and "using" make sense on the plot.  The
> data in the file is 0 1 2 3 4 5 6 7 8 9 and both the red and green plots
> are obviously treating the data as
> 
> (0,1)
> (2,3)
> (4,5)
> (6,7)
> (8,9)
> 
> in "test-4.png".
> 
> OK, so a couple strange things there, using "0" starting at -1 and a
> complaint about running out of data when there really shouldn't be.  Let
> me work on this...
> 
> Dan
> 

And since "cat test-4.gp outd.data out.data outd.data | gnuplot  WORKS" it
*seems* to be (a) reading exactly twice as much data for the first 5x2 record as
it should and then (b) is happy with a normal amount of data in the second 5x2
record.  This behavior is strange enough that I can't really understand how to
work around it. And I looked at datafile.c and the parsing is very powerful and
very hairy.  Trying to think in "clever c" and "clever haskell" in the same day
is giving me mental whiplash.

-- 
Chris