How to do a scatter plot with empty circles in Python?

0 votes
asked Nov 10, 2010 by eol

In Python, with Matplotlib, how can a scatter plot with empty circles be plotted? The goal is to draw empty circles around some of the colored disks already plotted by scatter(), so as to highlight them, ideally without having to redraw the colored circles.

4 Answers

0 votes
answered Nov 10, 2010 by gary-kerr

From the documentation for scatter:

Optional kwargs control the Collection properties; in particular:

        The string ‘none’ to plot faces with no outlines
        The string ‘none’ to plot unfilled outlines

Try the following:

import matplotlib.pyplot as plt 
import numpy as np 

x = np.random.randn(60) 
y = np.random.randn(60)

plt.scatter(x, y, s=80, facecolors='none', edgecolors='r')

example image

Note: For other types of plots see this post on the use of markeredgecolor and markerfacecolor.

0 votes
answered Nov 10, 2010 by whatnick

So I assume you want to highlight some points that fit a certain criteria. You can use Prelude's command to do a second scatter plot of the hightlighted points with an empty circle and a first call to plot all the points. Make sure the s paramter is sufficiently small for the larger empty circles to enclose the smaller filled ones.

The other option is to not use scatter and draw the patches individually using the circle/ellipse command. These are in matplotlib.patches, here is some sample code on how to draw circles rectangles etc.

0 votes
answered Nov 23, 2010 by denis

Here's another way: this adds a circle to the current axes, plot or image or whatever :

from matplotlib.patches import Circle  # $matplotlib/

def circle( xy, radius, color="lightsteelblue", facecolor="none", alpha=1, ax=None ):
    """ add a circle to ax= or current axes
        # from .../pylab_examples/
    e = Circle( xy=xy, radius=radius )
    if ax is None:
        ax = pl.gca()  # ax = subplot( 1,1,1 )
    e.set_edgecolor( color )
    e.set_facecolor( facecolor )  # "none" not None
    e.set_alpha( alpha )

alt text

(The circles in the picture get squashed to ellipses because imshow aspect="auto" ).

0 votes
answered Sep 15, 2017 by salvatore-cosentino

In matplotlib 2.0 there is a parameter called fillstyle which allows better control on the way markers are filled. In my case I have used it with errorbars but it works for markers in general

fillstyle accepts the following values: [‘full’ | ‘left’ | ‘right’ | ‘bottom’ | ‘top’ | ‘none’]

There are two important things to keep in mind when using fillstyle,

1) If mfc is set to any kind of value it will take priority, hence, if you did set fillstyle to 'none' it would not take effect. So avoid using mfc in conjuntion with fillstyle

2) You might want to control the marker edge width (using markeredgewidth or mew) because if the marker is relatively small and the edge width is thick, the markers will look like filled even though they are not.

Following is an example using errorbars:

myplot.errorbar(x=myXval, y=myYval, yerr=myYerrVal, fmt='o', fillstyle='none', ecolor='blue',  mec='blue')
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