Using matplotlib to annotate certain points

Question

While I can hack together code to draw an XY plot, I want some additional stuff:

Vertical lines that extend from the X axis to a specified distance upward
text to annotate that point, proximity is a must (see the red text)
the graph to be self-contained image: a 800-long sequence should occupy 800 pixels in width (I want it to align with a particular image as it is an intensity plot)

enter image description here

How do I make such a graph in mathplotlib?

I don't quite follow your 3rd point, do you mean you want to specify the size of the saved image, or to crop the axis off, or something else? — fraxel
– fraxel, Commented May 8, 2012 at 14:28
Isn't this matplotlib.sourceforge.net/api/… what you want ? — segasai
– segasai, Commented May 8, 2012 at 15:10
In my specific case, I want it (intensity projection of a source image) to fit an 800*600 space, just below the 800*600 source image — Jesvin Jose
– Jesvin Jose, Commented May 8, 2012 at 15:42
savefig, takes figsize, and dpi arguments. So you can set the size no probs, also you'll probably want to turn the axes off. — fraxel
– fraxel, Commented May 8, 2012 at 15:56
This would introduce scaling artifacts and might look extremely ugly. — hochl
– hochl, Commented May 8, 2012 at 16:05

Jesvin Jose · Accepted Answer · 2012-05-24 14:00:31Z

7

You can do it like this:

import matplotlib.pyplot as plt

fig = plt.figure()
ax = fig.add_subplot(1, 1, 1)
data = (0, 2, 3, 5, 5, 5, 9, 7, 8, 6, 6)
ax.plot(data, 'r-', linewidth=4)

plt.axvline(x=5, ymin=0, ymax=4.0 / max(data), linewidth=4)
plt.text(5, 4, 'your text here')
plt.show()

Note, that somewhat strangely the ymin and ymax values run from 0 to 1, so require normalising to the axis

enter image description here

EDIT: The OP has modified the code to make it more OO:

fig = plt.figure()
data = (0, 2, 3, 5, 5, 5, 9, 7, 8, 6, 6)

ax = fig.add_subplot(1, 1, 1)
ax.plot(data, 'r-', linewidth=4)
ax.axvline(x=5, ymin=0, ymax=4.0 / max(data), linewidth=4)
ax.text(5, 4, 'your text here')
fig.show()

edited May 24, 2012 at 14:00

Jesvin Jose

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answered May 8, 2012 at 14:14

fraxel

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