CODEWITHSUNDEEP
pythonmatplotlib
Matteo NNZ
Matteo NNZ

Reputation: 12665

Signal specific points in matplotlib

Having a basic chart like the following:

import matplotlib.pyplot as plt
import numpy as np

y = np.array([1,2,3,4,5,6])
f, ax = plt.subplots()
ax.plot(y)
plt.show()

... is there any way to create a little arrow, let's say, into the obs-points "3" and "5"? I have this need because I work with financial series and I would like to highlight with small arrows the points in which some events happened (according to a list of boolean occurrencies True/False). So, in the case I've asked above, the occurrency list would be [False, False, True, False, True, False] but I guess for this it's enough to multiply the vector by the original array so that I would get the markers at the right height. Here is a more complex web example to give the visual idea. Thanks in advance

Upvotes: 1

Views: 1173

Answers (1)

Ffisegydd
Ffisegydd

Reputation: 53698

In matplotlib you can use text annotations to annotate your graph suitably. The code below shows a simple example where I have annotated the third point in your linear plot. Obviously if you were to do this in your own code you could provide a more intelligent way of picking x,y coordinations of the arrow point and the text.

import matplotlib.pyplot as plt
import numpy as np

y = np.array([1,2,3,4,5,6])

f, ax = plt.subplots()

ax.plot(y, linestyle='None', marker='o')


for i in [2, 3, 4]:
    ax.annotate('', xy=(i-1, i), xytext=(i-1,i+0.5),
                arrowprops=dict(facecolor='black',
                                width=1,
                                shrink=0.1))

plt.margins(0.1)
plt.show()

EDIT I have modified the code to remove the text annotation to an empty string.

Example plot

Upvotes: 2

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