Manually set legend colors using matplotlib Python

Question

I try to plot the following line plot, but I have difficulties to manually set legend colors. Currently the legend colors did not match the line colors. Any help would be very helpful. Thank you.

import random
import matplotlib.pyplot as plt
random.seed(10)

data=[(i, i+random.randint(1,20), random.choice(list("ABC"))) for i in range(2000,2025)]

plt.figure(figsize=(14,8))
for x, y,z in data:
    a=(x,x+y)
    b=(y+random.random(),y+random.random())
    if z=="A":
        a=(x,x)
        plt.plot(a,b,"bo",linestyle="-", linewidth=0.4, color="blue")
    elif z=="B":
        plt.plot(a,b,"bo",linestyle="-", linewidth=0.4, color="green")
    else:
        plt.plot(a,b,"bo",linestyle="-", linewidth=0.4, color="red")
ax = plt.gca()
plt.legend(['A', 'B',"C"])

Answer 1

For custom generation of legends you can use this link.Composing Custom Legends

from matplotlib.patches import Patch
from matplotlib.lines import Line2D

legend_elements = [Line2D([0], [0], color='b', lw=4, label='Line'),
                   Line2D([0], [0], marker='o', color='w', label='Scatter',
                          markerfacecolor='g', markersize=15),
                   Patch(facecolor='orange', edgecolor='r',
                         label='Color Patch')]

# Create the figure
fig, ax = plt.subplots()
ax.legend(handles=legend_elements, loc='center')

plt.show()

Output will be like this: Output

Answer 2

You can create symbols as you add data to the plot, and then vet the legend to unique entries, like so:

import random
import matplotlib.pyplot as plt
random.seed(10)

data=[(i, i+random.randint(1,20), random.choice(list("ABC"))) for i in range(2000,2025)]

plt.figure(figsize=(14,8))
for x, y,z in data:
    a=(x,x+y)
    b=(y+random.random(),y+random.random())
    if z=="A":
        a=(x,x)
        plt.plot(a,b, '-o', linewidth=0.4, color="blue", label='A')
    elif z=="B":
        plt.plot(a,b, '-o', linewidth=0.4, color="green", label='B')
    else:
        plt.plot(a,b, '-o', linewidth=0.4, color="red", label='C')

        

symbols, names = plt.gca().get_legend_handles_labels()
new_symbols, new_names = [], []
for name in sorted(list(set(names))):
    index = [i for i,n in enumerate(names) if n==name][0]
    new_symbols.append(symbols[index])
    new_names.append(name)
    
plt.legend(new_symbols, new_names)