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I want to make a scatterplot (using matplotlib) where the points are shaded according to a third variable. I’ve got very close with this:
plt.scatter(w, M, c=p, marker="s")
where w and M are the data points and p is the variable I want to shade with respect to.
However I want to do it in greyscale rather than colour. Can anyone help?
There’s no need to manually set the colors. Instead, specify a grayscale colormap…
import numpy as np import matplotlib.pyplot as plt # Generate data... x = np.random.random(10) y = np.random.random(10) # Plot... plt.scatter(x, y, c=y, s=500) plt.gray() plt.show()
Or, if you’d prefer a wider range of colormaps, you can also specify the
cmap kwarg to
scatter. To use the reversed version of any of these, just specify the “
_r” version of any of them. E.g.
gray_r instead of
gray. There are several different grayscale colormaps pre-made (e.g.
import matplotlib.pyplot as plt import numpy as np # Generate data... x = np.random.random(10) y = np.random.random(10) plt.scatter(x, y, c=y, s=500, cmap='gray') plt.show()
In matplotlib grey colors can be given as a string of a numerical value between 0-1.
Then you can convert your third variable in a value inside this range and to use it to color your points.
In the following example I used the y position of the point as the value that determines the color:
from matplotlib import pyplot as plt x = [1, 2, 3, 4, 5, 6, 7, 8, 9] y = [125, 32, 54, 253, 67, 87, 233, 56, 67] color = [str(item/255.) for item in y] plt.scatter(x, y, s=500, c=color) plt.show()
Sometimes you may need to plot color precisely based on the x-value case. For example, you may have a dataframe with 3 types of variables and some data points. And you want to do following,
- Plot points corresponding to Physical variable ‘A’ in RED.
- Plot points corresponding to Physical variable ‘B’ in BLUE.
- Plot points corresponding to Physical variable ‘C’ in GREEN.
In this case, you may have to write to short function to map the x-values to corresponding color names as a list and then pass on that list to the
x=['A','B','B','C','A','B'] y=[15,30,25,18,22,13] # Function to map the colors as a list from the input list of x variables def pltcolor(lst): cols= for l in lst: if l=='A': cols.append('red') elif l=='B': cols.append('blue') else: cols.append('green') return cols # Create the colors list using the function above cols=pltcolor(x) plt.scatter(x=x,y=y,s=500,c=cols) #Pass on the list created by the function here plt.grid(True) plt.show()