Creating labels where line appears in matplotlib figure

Question

I have a figure created in matplotlib (time-series data) over which are a series of

matplotlib.pyplot.axvline

lines. I would like to create labels on the plot that appear close to (probably on the RHS of the line and towards the top of the figure) these vertical lines.

relevant, and with a nice answer: http://stackoverflow.com/questions/16992038/inline-labels-in-matplotlib — 0 _, Apr 19 '15 at 01:24
I've posted solution for this in the following [link](http://stackoverflow.com/a/35538091/5448887) — Tomer Nussbaum, Feb 21 '16 at 15:45

score 121 · Accepted Answer · answered Nov 16 '12 at 14:14

121

You can use something like

plt.axvline(10)
plt.text(10.1,0,'blah',rotation=90)

you might have to play around with the x and y value in text to get it to align properly. You can find the more complete documentation here.

answered Nov 16 '12 at 14:14

Dan

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If you want to use data coordinates for the x-axis and axis coordinates for the y-axis, you can place the text at x=10.1 and at 50% of the height using: `ax.text(10.1, 0.5, 'blah', rotation=90, transform=ax.get_xaxis_text1_transform(0)[0])` – Maximilian Mordig Apr 02 '21 at 09:47
Link is outdated. – zabop Apr 20 '21 at 19:12
If you get a "image size of … pixels is too large" error, check that your coordinates are within the y axis range (https://stackoverflow.com/a/52376517/812102). – Skippy le Grand Gourou Jul 24 '23 at 09:04

score 31 · Answer 2 · edited Sep 17 '20 at 02:16

A solution without manual placement is to use "blended transformations".

Transformations transform coordinates from one coordinate system to another. By specifying a transformation through the transform parameter of text, you can give the x and y coordinates of the text in the axis coordinate system (going from 0 to 1 from left to right/top to bottom of the x/y axes, respectively). With blended transformations, you can used a mixed coordinate system.

This is exactly what you need: you have the x coordinate given by the data and you want to place the text on the y axes somewhere relative to the axis, say in the center. The code to do this looks like this:

import matplotlib.transforms as transforms
import matplotlib.pyplot as plt

fig, ax = plt.subplots()

# the x coords of this transformation are data, and the
# y coord are axes
trans = ax.get_xaxis_transform()

x = 10
ax.axvline(x)
plt.text(x, .5, 'hello', transform=trans)

plt.show()

Creating labels where line appears in matplotlib figure

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