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I can manually add a label next to an arrow in Matplotlib 3.4.3. by estimating its location.

import matplotlib.pyplot as plt
W, H = 2, 3
offsetX = 0.1*W

arrow_style = {"head_width":0.1, "head_length":0.2, "color":"k"}
plt.arrow(x=0, y=0, dx=W, dy=H, **arrow_style)
plt.text(x=W/2+offsetX, y=H/2, s="U")
plt.show()

Output:

enter image description here

I wonder if there is a builtin way to add the label to an arrow and align its label accordingly? if no what is the easiest approach?

Iyach tharwa nambarek
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  • Does this answer your question? [Arrow properties in matplotlib annotate](https://stackoverflow.com/q/44489900/7758804). Otherwise, just the the way you have done it. – Trenton McKinney Oct 01 '21 at 16:39
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    Either your current way, or the way in the link. That's how you do it. There's not another way to align the text with the line. [`.text`](https://matplotlib.org/stable/api/_as_gen/matplotlib.pyplot.text.html) should have a `rotation` parameter though. – Trenton McKinney Oct 01 '21 at 16:51
  • @TrentonMcKinney: I can't find the way! – Iyach tharwa nambarek Oct 01 '21 at 20:37

1 Answers1

2

Maybe a bit easier to read using axes.annotate but somewhat equivalent to the code you've written:

import matplotlib.pyplot as plt

W, H = 2, 3
arrow_style = {
    "head_width": 0.1,
    "head_length": 0.2,
    "color":"k"
}

plt.arrow(x=0, y=0, dx=W, dy=H, **arrow_style)
plt.annotate('U',
             xy=(W/2, H/2),
             xytext=(10, -10),
             textcoords='offset points')
plt.show()

where:

  • xy is the point (x, y) to annotate
  • xytext is the position (x, y) to place the text at (default: xy). The coordinate system is determined by textcoords.
  • textcoords is the coordinate system that xy is given in ('offset points' means the offset in points from the xy value)

So in short, 10 points to the right and 10 points down from the center of the arrow.

Davide Madrisan
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