I cannot find a way to draw an arbitrary line with matplotlib
Python library. It allows to draw horizontal and vertical lines (with matplotlib.pyplot.axhline
and matplotlib.pyplot.axvline
, for example), but i do not see how to draw a line through two given points (x1, y1)
and (x2, y2)
. Is there a way? Is there a simple way?
You can plot a horizontal line in matplotlib python by either using the plot() function and giving a vector of the same values as the y-axis value-list or by using the axhline() function of matplotlib. pyplot that accepts only the constant y value.
In Python, the new line character “\n” is used to create a new line. When inserted in a string all the characters after the character are added to a new line. Essentially the occurrence of the “\n” indicates that the line ends here and the remaining characters would be displayed in a new line.
This will draw a line that passes through the points (-1, 1) and (12, 4), and another one that passes through the points (1, 3) et (10, 2)
x1 are the x coordinates of the points for the first line, y1 are the y coordinates for the same -- the elements in x1 and y1 must be in sequence.
x2 and y2 are the same for the other line.
import matplotlib.pyplot as plt x1, y1 = [-1, 12], [1, 4] x2, y2 = [1, 10], [3, 2] plt.plot(x1, y1, x2, y2, marker = 'o') plt.show()
I suggest you spend some time reading / studying the basic tutorials found on the very rich matplotlib website to familiarize yourself with the library.
[edit]:
As shown by @thomaskeefe, starting with matplotlib 3.3, this is now builtin as a convenience: plt.axline((x1, y1), (x2, y2))
, rendering the following obsolete.
There are no direct ways to have lines extend to infinity... matplotlib will either resize/rescale the plot so that the furthest point will be on the boundary and the other inside, drawing line segments in effect; or you must choose points outside of the boundary of the surface you want to set visible, and set limits for the x and y axis.
As follows:
import matplotlib.pyplot as plt x1, y1 = [-1, 12], [1, 10] x2, y2 = [-1, 10], [3, -1] plt.xlim(0, 8), plt.ylim(-2, 8) plt.plot(x1, y1, x2, y2, marker = 'o') plt.show()
I was checking how ax.axvline does work, and I've written a small function that resembles part of its idea:
import matplotlib.pyplot as plt import matplotlib.lines as mlines def newline(p1, p2): ax = plt.gca() xmin, xmax = ax.get_xbound() if(p2[0] == p1[0]): xmin = xmax = p1[0] ymin, ymax = ax.get_ybound() else: ymax = p1[1]+(p2[1]-p1[1])/(p2[0]-p1[0])*(xmax-p1[0]) ymin = p1[1]+(p2[1]-p1[1])/(p2[0]-p1[0])*(xmin-p1[0]) l = mlines.Line2D([xmin,xmax], [ymin,ymax]) ax.add_line(l) return l
So, if you run the following code you will realize how does it work. The line will span the full range of your plot (independently on how big it is), and the creation of the line doesn't rely on any data point within the axis, but only in two fixed points that you need to specify.
import numpy as np x = np.linspace(0,10) y = x**2 p1 = [1,20] p2 = [6,70] plt.plot(x, y) newline(p1,p2) plt.show()
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