How do you add a line to a scatter plot in python?

I am using python's matplotlib and want to create a matplotlib.scatter() with additional line. The line should proceed from the lower left corner to the upper right corner independent of the scatters content. A linear regression through the data, like in this post, is not what I am looking for. Also it should be dynamically and independent of the scatter input.

This should be the final plot:

EDIT:

Doing this got me the result:

# Scatter Plot
x = data_calc_hourly.temp
y =  data_obs_hourly.temp

lineStart = data_calc_hourly.temp.min() 
lineEnd = data_calc_hourly.temp.max()  

plt.figure()
plt.scatter(x, y, color = 'k', alpha=0.5)
plt.plot([lineStart, lineEnd], [lineStart, lineEnd], 'k-', color = 'r')
plt.xlim(lineStart, lineEnd)
plt.ylim(lineStart, lineEnd)
plt.show()

Is there any better way ?

asked Nov 9, 2016 at 21:54

4

This draws a diagonal line which is independent of the scatter plot data and which stays rooted to the axes even if you resize the window:

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.lines as mlines
import matplotlib.transforms as mtransforms

x, y = np.random.random((2, 100))*2
fig, ax = plt.subplots()
ax.scatter(x, y, c='black')
line = mlines.Line2D([0, 1], [0, 1], color='red')
transform = ax.transAxes
line.set_transform(transform)
ax.add_line(line)
plt.show()

answered Nov 9, 2016 at 22:15

unutbuunutbu

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2

Besides unutbu's answer one other option is to get the limits of the axis after you ploted the data and to use them to add the line. After this you will still need to change back the axis limits as they would change with the addition of the line:

# Scatter Plot
x = data_calc_hourly.temp
y =  data_obs_hourly.temp

lineStart = data_calc_hourly.temp.min() 
lineEnd = data_calc_hourly.temp.max()  

plt.figure()
plt.scatter(x, y, color = 'k', alpha=0.5)
y_lim = plt.ylim()
x_lim = plt.xlim()
plt.plot(x_lim, y_lim, 'k-', color = 'r')
plt.ylim(y_lim)
plt.xlim(x_lim)
plt.show()

answered Mar 1, 2019 at 10:05

João AlmeidaJoão Almeida

3,9372 gold badges18 silver badges35 bronze badges

0

I have tried updating the min and max limits for the cases where X and Y axis have different max and min data.

x = data_calc_hourly.temp
y =  data_obs_hourly.temp

calc_min = data_calc_hourly.temp.min()
calc_max = data_calc_hourly.temp.max()

obs_min = data_obs_hourly.temp.min()
obs_max = data_obs_hourly.temp.max()

lineStart = min(calc_min,obs_min)
lineEnd = max(calc_max,obs_max)

plt.figure()
plt.scatter(x, y, color = 'k', alpha=0.5)
plt.plot([lineStart, lineEnd], [lineStart, lineEnd], color = 'r')
plt.xlim(lineStart, lineEnd)
plt.ylim(lineStart, lineEnd)
plt.show()

answered Jul 18, 2021 at 14:56

JohnnyJohnny

1171 silver badge8 bronze badges

First, we can create a scatter for different data points using the scatter method, and then, we can plot the lines using the plot method.

Steps

• Create a new figure, or activate an existing figure with figure size(4, 3), using figure() method.

• Add an axis to the current figure and make it the current axes, create x using plt.axes().

• Draw scatter points using scatter() method.

• Draw line using ax.plot() method.

• Set the X-axis label using plt.xlabel() method.

• Set the Y-axis label using plt.ylabel() method.

• To show the plot, use plt.show() method.

Example

import random
import matplotlib.pyplot as plt

plt.figure(figsize=(4, 3))
ax = plt.axes()
ax.scatter([random.randint(1, 1000) % 50 for i in range(100)],
[random.randint(1, 1000) % 50 for i in range(100)])
ax.plot([1, 2, 4, 50], [1, 2, 4, 50])

ax.set_xlabel('x')
ax.set_ylabel('y')

plt.show()

Output

Updated on 17-Mar-2021 08:48:17

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