Stem plot in matplotlib?

Question

I want to plot(x, sin(x)) but instead of a line from (xi,yi) to (x_i+1,y_i+1) I want a vertical line to each point from (xi,0) to (xi,yi) as sometimes interpolation between the points makes no sense (e.g. quantized data) (and it looks much better with that vertical line than without).

Much like the stem plot below (from the matlab docs) but with the option of being able to turn off the circles and the "-" between points. Unfortunately, I couldn't find an appropriate plotting function in the matplotlib documentation myself.

stem plot

moooeeeep · Accepted Answer · 2019-04-17 06:42:19Z

19

There is a stem plot (a.k.a. lollipop plot) in the matplotlib as well.

Below you can find an example from the docs.

import matplotlib.pyplot as plt
import numpy as np

# returns 10 evenly spaced samples from 0.1 to 2*PI
x = np.linspace(0.1, 2 * np.pi, 10)

markerline, stemlines, baseline = plt.stem(x, np.cos(x), '-.')

# setting property of baseline with color red and linewidth 2
plt.setp(baseline, color='r', linewidth=2)

plt.show()

stem plot

If you want to adjust the y-position of the baseline, you can use the bottom parameter.

(adapted) Example:

import matplotlib.pyplot as plt
import numpy as np

# returns 10 evenly spaced samples from 0.1 to 2*PI
x = np.linspace(0.1, 2 * np.pi, 10)

plt.stem(x, np.cos(x), '-.', bottom=-2)

plt.show()

stem plot 2

edited Apr 17, 2019 at 6:42

answered Oct 30, 2012 at 18:26

moooeeeep

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6 Comments

arynaq Over a year ago

Thanks now I need to figure out how to remove the blue circles.

moooeeeep Over a year ago

@user948652 you only need to set the markerfmt parameter appropriately, e.g. markerfmt='.'. Just have a look at the documentation of the call parameters, it's nicely explained there.

endolith Over a year ago

is there a way to start the stems at negative infinity, though? I want something like this: namoseley.files.wordpress.com/2012/09/…

moooeeeep Over a year ago

@endolith You can use the bottom parameter to specify the y-position of the baseline.

endolith Over a year ago

@moooeeeep: Must be new? stem() got an unexpected keyword argument 'bottom'

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reptilicus · Accepted Answer · 2012-10-30 18:21:16Z

0

I think you want to use linestyle='steps--'

plot(x, sin(x), linestyle='steps--')

answered Oct 30, 2012 at 18:21

reptilicus

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2 Comments

arynaq Over a year ago

This is a horizontal step plot, doesn't do vertical lines like in the .gif link

reptilicus Over a year ago

My bad, I think @moooeeeep has it

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