programmatically change matplotlib fill data

Question

I'm creating an animation using Matplotlib and I'm using a Fill object. I'd like to be able to change the fill data from a function. For other plot types there's usually a set_data() function or set_offsets(). Fill doesn't seem to have one. I would expect to do something like the code below but this doesn't work. Any ideas?

import matplotlib.pyplot as plt
fig = plt.figure()
ax = plt.axes(xlim=(-1, 1), ylim=(-1, 1),)
triangle, = ax.fill([0,1,1],[0,0,1])
# I want to change the datapoints later in my code, like this:
triangle.set_data([0,2,2],[0,0,2])

What type of object is triangle? Did you look up the documentation for that type? I can understand why you would want that code to work, but why do you think it should? — tacaswell
– tacaswell, Commented May 2, 2014 at 14:49
triangle is a fill object, which is a Polygon, which I would think would have a way to change it's data. — gallamine
– gallamine, Commented May 2, 2014 at 17:27
Did you look at matplotlib.org/api/artist_api.html#matplotlib.patches.Polygon ? — tacaswell
– tacaswell, Commented May 2, 2014 at 17:41
Yes. Not obvious if there's a way to change the data. Hence my question. I'd be open to another suggestion for manipulating the data to a closed,filled, object. — gallamine
– gallamine, Commented May 2, 2014 at 18:38

tacaswell · Accepted Answer · 2014-05-02 19:34:48Z

2

This is not particularly well documented, but Polygon objects have a pair of methods get_xy and set_xy. The method get_xy() returns an ndarray with shape (N + 1, 2). The extra point is a repeat of the first point (so that the polygon is closed). Putting the desired data into the expected format (which is what is specified in the documentation to construct a Polygon object):

triangle.set_xy(np.array([[0, 2, 2, 0],[0, 0, 2, 0]]).T)
ax = plt.gca()
ax.set_xlim([0, 3])
ax.set_ylim([0, 3])
plt.draw()

This even lets you change the number of vertices in your patch.

Added issue to clarify the documentation https://github.com/matplotlib/matplotlib/issues/3035.

answered May 2, 2014 at 19:34

tacaswell

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