matplotlib-users

[Matplotlib-users] clipping feature?

[James B. <bo...@ll...>]

If I set the axis limits to a value less than the actual domain of the 
data, the line is not extended to the edge of the plot but rather is 
only drawn to the final point within the domain. The following 
illustrates what I mean:

ax = subplot(111)
plot([1,2,3,4],'bo', [1,2,3,4],'k')
axis([0.,2.4,1.,4.])

The plot stops at the point (2,3) although the data go to (3,4). When I 
have dealt with these issues, I usually draw the line to its full 
extent and then clip the line so it stops at the edge of the plot 
frame.

I set the axis bounds when I am plotting a number of lines some of 
which have a larger domain. While interested in the behaviour in the 
limited domain, I would like to retain the information that some lines 
extend beyond.
When I first encountered this behaviour, I thought that I had 
mistakenly truncated my input data - I think that the plot should show 
as much of the data passed to it as possible.

Is there something I am missing - or is this a feature?

JIm

Re: [Matplotlib-users] clipping feature?

[John H. <jdh...@ac...>]

>>>>> "James" == James Boyle <bo...@ll...> writes:

    James> I set the axis bounds when I am plotting a number of lines
    James> some of which have a larger domain. While interested in the
    James> behaviour in the limited domain, I would like to retain the
    James> information that some lines extend beyond.  When I first
    James> encountered this behaviour, I thought that I had mistakenly
    James> truncated my input data - I think that the plot should show
    James> as much of the data passed to it as possible.

    James> Is there something I am missing - or is this a feature?

It's a feature!

matplotlib does two kinds of clipping: data clipping and viewport
clipping.  Viewport clipping is the typical clipping where the lines
are clipped to the viewport.  data clipping throws out all points not
in the viewport.

I work with very long data sets of which only a small portion is in
the viewport, and use the interactive navigation controls to scroll
trough it.  I found it was much more efficient to first clip the data
with Numeric before plotting it.  See examples/stock_demo.py, of which
only a few days of 60 days of data are initially in the viewport.

You can control this in a couple of ways:

    from matplotlib.matlab import *
    ax = subplot(111)
    line1, line2 = plot([1,2,3,4],'bo', [1,2,3,4],'k')
    line1.set_data_clipping(False)
    line2.set_data_clipping(False)
    axis([0.,2.4,1.,4.])
    show()

Or edit the init function of lines.Line2D to turn data clipping off by
default

        self._useDataClipping = False

I've been meaning to make a matplotlibrc file to control things like
default line width, color, fontsize and name, antialiasing, data
clipping and so on.

JDH

Re: [Matplotlib-users] clipping feature?

[matthew a. <ma...@ca...>]

I suggest to John a while back that for plotting it makes more sense for 
data ranges to be inclusive 

[] or min <= x <= max

rather than half-inclusive 

[) or min <= x < max

as is the python default for functions like range().

Specifically, what about making the default behaviour to clip the data at
the first point which is equal or greater than the axis range? That should
maintain the efficiency gains of clipping, while still keeping the
scientific plotting behaviour that I think most users are accustomed to.

Cheers,
Matthew.

Re: [Matplotlib-users] clipping feature?

[John H. <jdh...@ac...>]

>>>>> "matthew" == matthew arnison <ma...@ca...> writes:

    matthew> Specifically, what about making the default behaviour to
    matthew> clip the data at the first point which is equal or
    matthew> greater than the axis range? That should maintain the
    matthew> efficiency gains of clipping, while still keeping the
    matthew> scientific plotting behaviour that I think most users are
    matthew> accustomed to.

Hi Matthew -

That's a good idea - the data clipping feature was a gotcha for many.
For the next release, I turned data clipping off by default since I
don't think it's the typical use case and implemented the "first point
which is equal or greater" suggestion.  However, I also have created a
config file, so you can set the default as you like.

JDH 

[Matplotlib-users] how to set the legend location?

[matthew a. <ma...@ca...>]

Hi

Now that we have the lovely new syntax for setting legend labels for each 
line:

plot(x, sin(x), label='sin(x)')
plot(x, cos(x), label='cos(x)')

how do we then move the legend from the default upper right location?

legend()

turns the legend on, but the LOC argument has to be second or third, after 
the LINES and/or LABELS. What about a new loc keyword for legend? E.g.

legend(loc=5)

While we're talking about problems inherited from matlab's use of
positional arguments, is there some easy way to set the x or y axis limits
without setting the other axis? E.g. if I want to leave the x axis
automatic, but manually set the y axis?

I looked at help(axis) and at 

http://matplotlib.sourceforge.net/matlab_commands.html

and I couldn't see anything obvious like xaxis or yaxis functions.

This works:

autoaxis = axis()
autoaxis[2:4] = (ymin, ymax)
axis(autoaxis)

but what if I add a plot afterwards that changes the x axis limits?

And it seems like hard work compared to:

yaxis(ymin, ymax)

Cheers,
Matthew.