Thread: [matplotlib-devel] colorcycles and empty data

Just had a thought and I am curious about what others think.

Now that we have agreed that calling a plotting function with empty data
should always be considered valid, should it also automatically advance the
colorcycle?  I think it should.

Here is a use-case: consider a user who is plotting temperature in three
regions over time in one subplot, and surface pressure over time for those
same three regions.  Let's say the thermometer in second region started
reporting only NaNs.  If empty data did not advance the color cycle, then
the line for the temperature plot of the third region will be same as the
line for the pressure plot for the second region, leading to mis-leading
interpretation that the thermometer in the third region was the one that
broke.

This is a really simple example, but I can see this being harder to ensure
for more complicated plots the depend on the automatic color cycling.

Ben Root

On 04/01/2011 10:47 AM, Benjamin Root wrote:
> Just had a thought and I am curious about what others think.
>
> Now that we have agreed that calling a plotting function with empty data
> should always be considered valid, should it also automatically advance
> the colorcycle?  I think it should.

I agree.  Fortunately, that is the present behavior, at least with this 
simple test:

plot([1,2,3])
plot([], [])
plot([3,2,1])

Eric


>
> Here is a use-case: consider a user who is plotting temperature in three
> regions over time in one subplot, and surface pressure over time for
> those same three regions.  Let's say the thermometer in second region
> started reporting only NaNs.  If empty data did not advance the color
> cycle, then the line for the temperature plot of the third region will
> be same as the line for the pressure plot for the second region, leading
> to mis-leading interpretation that the thermometer in the third region
> was the one that broke.
>
> This is a really simple example, but I can see this being harder to
> ensure for more complicated plots the depend on the automatic color cycling.
>
> Ben Root
>
>
>
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On Fri, Apr 1, 2011 at 4:46 PM, Eric Firing <ef...@ha...> wrote:

> On 04/01/2011 10:47 AM, Benjamin Root wrote:
> > Just had a thought and I am curious about what others think.
> >
> > Now that we have agreed that calling a plotting function with empty data
> > should always be considered valid, should it also automatically advance
> > the colorcycle?  I think it should.
>
> I agree.  Fortunately, that is the present behavior, at least with this
> simple test:
>
> plot([1,2,3])
> plot([], [])
> plot([3,2,1])
>
> Eric
>
>
Ok, good to know that someone else agrees.  Enforcing this would probably
best be done through tests that explicitly tests for this in a variety of
different kinds of plots.  Looks like yet another thing to add to my todo
list when I finish my current "distraction".

Ben Root