Elegant way to match a string to a random color matplotlib

Question

I want to translate the labels of some data to colors for graphing with matplotlib

I have a list of names ["bob", "joe", "andrew", "pete"]

Is there a built in way to map these strings with color values in matplotlib? I thought about randomly creating hex values but I could end up with similar colors or non visible colors.

I've tried a couple different ways of trying to create key values from the below cmap answer:

this:

#names is a list of distinct names
cmap = plt.get_cmap('cool')
colors = cmap(np.linspace(0, 1, len(names)))
clr = {names[i]: colors[i] for i in range(len(names))}
ax.scatter(x, y, z, c=clr)

Answer 1

Choose a color map, such as viridis:

cmap = plt.get_cmap('viridis')

The colormap, cmap, is a function which can take an array of values from 0 to 1 and map them to RGBA colors. np.linspace(0, 1, len(names)) produces an array of equally spaced numbers from 0 to 1 of length len(names). Thus,

colors = cmap(np.linspace(0, 1, len(names)))

selects equally-spaced colors from the viridis color map.

Note that this is not using the value of the string, it only uses the ordinal position of the string in the list to select a color. Note also that these are not random colors, this is just an easy way to generate unique colors from an arbitrary list of strings.

---

So:

import numpy as np
import matplotlib.pyplot as plt

cmap = plt.get_cmap('viridis')
names = ["bob", "joe", "andrew", "pete"]
colors = cmap(np.linspace(0, 1, len(names)))
print(colors)
# [[ 0.267004  0.004874  0.329415  1.      ]
#  [ 0.190631  0.407061  0.556089  1.      ]
#  [ 0.20803   0.718701  0.472873  1.      ]
#  [ 0.993248  0.906157  0.143936  1.      ]]

x = np.linspace(0, np.pi*2, 100)
for i, (name, color) in enumerate(zip(names, colors), 1):
    plt.plot(x, np.sin(x)/i, label=name, c=color)
plt.legend()
plt.show()

---

The problem with

clr = {names[i]: colors[i] for i in range(len(names))}
ax.scatter(x, y, z, c=clr)

is that the c parameter of ax.scatter expects a sequence of RGB(A) values of the same length as x or a single color. clr is a dict, not a sequence. So if colors is the same length as x then you could use

ax.scatter(x, y, z, c=colors)

Answer 2

I use the hash function to get numbers between 0 and 1, you can use this even when you don't know all the labels:

x = [1, 2, 3, 4, 5]
labels = ["a", "a", "b", "b", "a"]
y = [1, 2, 3, 4, 5]

colors = [float(hash(s) % 256) / 256 for s in labels]      

plt.scatter(x, y, c=colors, cmap="jet")
plt.show()