How to plot 1-d data at given y-value with pylab

Question

I want to plot the data points that are in a 1-D array just along the horizontal axis [edit: at a given y-value], like in this plot:

How can I do this with pylab?

K.-Michael Aye · Accepted Answer · 2018-03-26T18:49:48.113

40

Staven already edited his post to include how to plot the values along y-value 1, but he was using Python lists.

A variant that should be faster (although I did not measure it) only uses numpy arrays:

import numpy as np
import matplotlib.pyplot as pp
val = 0. # this is the value where you want the data to appear on the y-axis.
ar = np.arange(10) # just as an example array
pp.plot(ar, np.zeros_like(ar) + val, 'x')
pp.show()

As a nice-to-use function that offers all usual matplotlib refinements via kwargs this would be:

def plot_at_y(arr, val, **kwargs):
    pp.plot(arr, np.zeros_like(arr) + val, 'x', **kwargs)
    pp.show()

edited Mar 26 '18 at 18:49

answered Mar 15 '12 at 15:37

K.-Michael Aye

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What is this function **zeros_like()**? Can you please define it. – Léo Léopold Hertz 준영 Jan 25 '14 at 12:16
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zeros_like is just like np.zeros() providing you an array filled with zeros, but with _like() it will assume the shape of the provided array. There's also a ones_like(), very handy – K.-Michael Aye Jan 25 '14 at 17:21

Staven · Answer 2 · 2011-09-09T17:51:47.447

25

This will plot the array "ar":

import matplotlib.pyplot as pp
ar = [1, 2, 3, 8, 4, 5]
pp.plot(ar)
pp.show()

If you are using ipython, you can start it with the "-pylab" option and it will import numpy and matplotlib automatically on startup, so you just need to write:

ar = [1, 2, 3, 8, 4, 5]
plot(ar)

To do a scatter plot with the y coordinate set to 1:

plot(ar, len(ar) * [1], "x")

edited Sep 09 '11 at 17:51

answered Sep 08 '11 at 18:08

Staven

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Hi, Thanks for the answer. This is the way I tried the first time, but may be I was not able to explain my question properly. The plot it draws is a continuous lines made by connecting points in ar. I have an 1-D array of 800 data values distributed in (-1,6). I just want to plot the points on a constant Y (http://static.inky.ws/image/644/image.jpg) but with the method you explained am getting something like this (http://static.inky.ws/image/645/image.jpg). – Nihar Sarangi Sep 09 '11 at 09:12
the first plot I got is with matlab, I want to do a similar plot with matplotlib. – Nihar Sarangi Sep 09 '11 at 09:17

score 0 · Answer 3 · edited May 26 '23 at 13:35

0

X = np.arange(10)

plt.scatter( X, [0] * X.shape[0])

edited May 26 '23 at 13:35

gboffi

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answered May 12 '22 at 05:55

jyostna bodapati

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If one wants to plot at a different _y_ level, `Yo = ... ; plt.scatter( X, [Yo] * X.shape[0])` --- maybe you want to [edit] your answer to incorporate my suggestion. – gboffi May 26 '23 at 13:38

How to plot 1-d data at given y-value with pylab

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