Question

Given coordinates of [1,5,7,3,5,10,3,6,8] for matplotlib.pyplot, how do I highlight or colour different segments of the line. For instance, the coordinates 1-3 ([1,5,7,3]) in the list represent attribute a. How do I colour this bit of the line and mark it in the legend?

Edit: The list in question contains tens of thousands of elements. I’m trying to highlights specific sections of the list. From the answers so far, is it right to assume I must draw each segment one by one? There isn’t a way to say “select line segment from x1 coord to x2 coord, change colour of line”

Answer 1

Yes, you need to redraw the line, but you can clip the line so that only the part you are interested in is visible. To do this I create a rectangle covering the area that represents prop (a), then I use this to create a clip_path.

import matplotlib.pyplot as plt
from matplotlib.transforms import Bbox

data = [1,5,7,3,5,10,3,6,8]
X0 = 1
X1 = 3

plt.plot(data, label='full results')
# make a rectangle that will be used to crop out everything not prop (a)
# make sure to use data 'units', so set the transform to transData
propArect = plt.Rectangle((X0, min(data)), X1, max(data), 
                          transform=plt.gca().transData)
# save the line so when can set the clip
line, = plt.plot(data,
         color='yellow',
         linewidth=8,
         alpha=0.5,
         label='Prop (a)',
         )
line.set_clip_path(propArect)

handles, labels = plt.gca().get_legend_handles_labels()
plt.legend(handles, labels)
plt.savefig('highlight.png')
plt.show()

This results in:

When I plotted the line segment, I adjusted the transparent-ness using the alpha keyword, which ranges from 0-1 or transparent to solid. I also made it a thicker line to extend beyond the original results.