[Octave-bug-tracker] [bug #47904] text() with the wrong sized vector or cell array gives unexpected/weird results

[anonymous]

URL:
  <http://savannah.gnu.org/bugs/?47904>

                 Summary: text() with the wrong sized vector or cell array
gives unexpected/weird results
                 Project: GNU Octave
            Submitted by: None
            Submitted on: Thu 12 May 2016 01:10:35 AM UTC
                Category: Plotting
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Other
                  Status: None
             Assigned to: None
         Originator Name: Peter Halasz
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 4.0.2
        Operating System: Microsoft Windows

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Details:

In my experience, filing a long or detailed bug report leads to fewer people
reading or responding to it, so I've including a TL;DR for the lazy.

TL;DR: see attached screenshots. There's little I've said below that isn't
summed up in the first screenshot.

I'm relatively new to Octave, but I was encouraged to report this when I was
helped on IRC. I'm not experienced enough to demand Octave's behaviour is
changed, but I can give you an idea of the experience which seems very
suboptimal. 

I made a minimal example and duplicated it four times with minimal changes to
show a comparison of different configurations. You can run it once at see
three random scatter plots with slightly different inputs.

The first subplot is 500 random points with 500 text labels, given as a 500x2
char vector (vector of strings). The 'x2' is because 2 characters is the max
length of a label in this example. Renders correctly.

The second is also 500 random points with 500 text labels, but this time given
as a cell array (500x1). Renders correctly.

The third is 500 random points with 499 text labels (to simulate an "off by
one" user error). Text data is given as a vector of strings (char 499x2). This
causes the first label text to be used for all labels, and the others to be
ignored. This behaviour seems kinda weird. Perhaps it's acceptable to do this
without a warning? I don't know.

The forth is 500 random points with 499 text labels, given as a cell array
(499x1). This causes all 499 labels to be rendered for every one of the 500
points. This takes around 20 seconds to render on Windows (i7 2600 / GTX 460).
This might be expectedly slow for Octave, but it is a performance issue, it's
difficult to debug the off-by-one user error because of the performance issue,
and it's very weird/unexpected behaviour even if it is vaguely documented to
do this (though I'm not sure if it is).

The code:


numberOfPoints = 500;

x = rand(numberOfPoints, 1);
y = rand(numberOfPoints, 1);
l = rand(numberOfPoints, 1) .* 10; # label data
labels = int2str(l);
cellLabels = cellstr(labels);

figure

subplot(1,4,1)
start = time();
scatter(x, y);
text(x, y, labels);
t = num2str(time()-start, '%1.3f');
ttext = ['500x2 char label data. Time: ' t]
title(ttext);

subplot(1,4,2)
start = time();
scatter(x, y);
text(x, y, cellLabels);
t = num2str(time()-start, '%1.3f');
ttext = ['500x1 cell label data. Time: ' t]
title(ttext);

subplot(1,4,3)
start = time();
scatter(x, y);
text(x, y, (labels(2:end, :))); # Oops! One label missing
t = num2str(time()-start, '%1.3f');
ttext = ['499x2 char label data. Time: ' t]
title(ttext);

subplot(1,4,4)
start = time();
scatter(x, y);
text(x, y, (cellLabels(2:end, :))); # Oops! One label missing
t = num2str(time()-start, '%1.3f');
ttext = ['499x1 cell label data. Time: ' t]
title(ttext);


A screenshot is attached of the output (awful_text_example_4_subplots.png).

The text output of the code (required, as one title is obscured in the
screenshot):


ttext = 500x2 char label data. Time: 4.399
ttext = 500x1 cell label data. Time: 4.393
ttext = 499x2 char label data. Time: 4.414
ttext = 499x1 cell label data. Time: 19.461


Some might say the output is expected and desired, but I'll steam roll ahead
and offer some suggestions to make the user experience better. Perhaps the
community could come up with something which better matches how Octave does
things and allows better backwards compatibility with existing code bases.
Mostly I hope this bug report might be a launching point for discussion which
motivates someone to develop Octave's code base further and make it a better
open source product.

Recommended fixes:

1. At a minimum: Display a warning to the user if there is a mismatch between
the number of labels and the number of data points when calling text(), unless
there is only one label and it is only one line in length.

2. Change the behaviour of text() so it treats cell arrays similarly to vector
arrays. i.e. create some consistency, although both behaviours seem bad when
there are mismatched input lengths.

3. Implement a separate function (or require an additional parameter) to
render the same lines of text multiple times (as what is currently default for
cell data), or to force data to be ignored (as what is currently default for
vector of strings input)

Those seem like the obvious answers, but perhaps the community could come up
with and agree to a better solution.

More general recommendations:

4. Improve rendering times. I don't know anything about the internals of
Octave's rendering engine, but I can't see why the first three examples should
take 4+ seconds to render. Coming from a game development background, drawing
500 anti-aliased circles with 2-character labels should take microseconds, not
seconds. If rendering times were improved, then debugging would become easier.
Removing 20 seconds from the debug cycle allows more experimentation by the
user. (See "Motivation / background" below for how this directly impacted my
debugging of this)

5. Use a separate thread to respond quickly to user input. Closing the "Figure
1" window should not take 20 seconds (as you wait for it to finish rendering).
And the software should not appear to be hung just because because you resized
a window.

6. Display an "Executing..." message with a barber's pole or something to tell
the user a script is still running and hasn't crashed.

7. Implement the table data type and readtable(), e.g. bug #44571 -- my
initial bug would have been unlikely to come up if I was importing data in a
uniform way. Instead I hacked together a couple of different methods to import
the text and numeric data from a CSV.

8. Prevent subplots from rendering outside of their area. I would have liked
to present my examples on a 2x2 subplot grid. :)

Motivation / background:

I was trying to draw a scatter plot of some CSV data I had generated
elsewhere. I'd accidentally left the heading row in some of the data and it
created a monstrosity (see real_world_example.png). When I was initially
trying to debug my code, as I didn't know the problem, I just saw a lot of
text filling up my scatter plot. So I reduced the number of labels from 512 to
just 50 so it would render fast enough that I could debug. Doing that also cut
down the clutter enough that I could see what it was actually going on (all
labels being rendered at all points). At some point I fixed the off-by-one
mismatch, but as I had cut down the number of labels being displayed, the
weird rendering continued. I assumed it was the data format of labels. I went
onto #octave to ask how to convert cells to a string array. IRC user jwe asked
the right questions and pointed out the size mismatch of the data, and then
encouraged me to file this bug report. I still don't know how to convert cell
data to a vector of strings. Thanks for reading. I hope this bug report
encourages you to work on improving Octave.



    _______________________________________________________

File Attachments:


-------------------------------------------------------
Date: Thu 12 May 2016 01:10:35 AM UTC  Name: awful_text_example_4_subplots.png
 Size: 838kB   By: None

<http://savannah.gnu.org/bugs/download.php?file_id=37134>
-------------------------------------------------------
Date: Thu 12 May 2016 01:10:35 AM UTC  Name: real_world_example.png  Size:
243kB   By: None

<http://savannah.gnu.org/bugs/download.php?file_id=37135>

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