如何从图中删除点？

Question

I am using matplotlib.pyplot.

I would like to do the following:

1. I want to plot a series of background dots (single blue dot in example).
2. I add an additional series of dots (3 black dots in example)
3. I save the figure
4. I remove the additional series of dots (black) and keep the background one (blue).

How can I perform step 4? I would like to avoid having to replot the background dots.

Hereunder is an example of code with step 4 missing.

import matplotlib.pyplot as plt

fig = plt.figure()

plt.xlim(-10,10)
plt.ylim(-10,10)

#step 1: background blue dot
plt.plot(0,0,marker='o',color='b')

#step 2: additional black dots
points_list = [(1,2),(3,4),(5,6)]
for point in points_list:
    plt.plot(point[0],point[1],marker='o',color='k')

#step 3: save
plt.savefig('test.eps')

#step 4: remove additional black dots

Answer 1

You can remove the plotted points by doing this :

temporaryPoints, = plt.plot(point[0],point[1],marker='o',color='k')
temporaryPoints.remove()

Answer 2

You can use:

#step 2
black_points, = plt.plot( zip(*points_list), marker="o", color="k")

#... step 3 ...
#...

#step 4
black_points.set_visible( False)

Answer 3

The plot function returns a list of Line2D objects which represent the plotted data. These objects have a remove method which will remove them from the figure they've been plotted on (note that Line2D inherits from Artist which you can check via Line2D.__mro__ ):

remove() method of matplotlib.lines.Line2D instance
    Remove the artist from the figure if possible.  The effect
    will not be visible until the figure is redrawn, e.g., with
    :meth:`matplotlib.axes.Axes.draw_idle`.  Call
    :meth:`matplotlib.axes.Axes.relim` to update the axes limits
    if desired.

    [...]

So you can do the following (I combined plotting the single points in one go):

points = plt.plot(*zip(*points_list), 'o', color='k')[0]
# Remove the points (requires redrawing).
points.remove()

Keeping your for loop this would be:

points = []
for point in points_list:
    points.extend(
        plt.plot(point[0], point[1], marker='o', color='k')
    )
for p in points:
    p.remove()

Or more concise using a list comprehension:

points = [plt.plot(*p, marker='o', color='k')[0] for p in points_list]