Matplotlib：如何将图例添加到散点图的颜色？

Question

我的数据框有三列SKU，保存和标签（categorical var）。当我打电话给plt.legend()时，它添加了“保存”的图例，但我想为我的颜色添加图例（a，b，c，d）？

from numpy import * 
import numpy as np 
import pandas as pd 
from matplotlib import pyplot as plt 
import matplotlib.pyplot as plt 

df = pd.DataFrame(np.random.rand(100,1), columns=['Saving']) 
df['SKU'] = np.arange(100) 
df['label'] = np.random.choice(['a', 'b', 'c','d'], 100) 

fig, ax = plt.subplots() 
colors = {'a':'red', 'b':'blue', 'c':'green', 'd':'white'} 
figSaving = ax.scatter(df['SKU'], df['Saving'], c=df['label'].apply(lambda x: colors[x])) 

plt.show() 

Answer 1

import pandas as pd 
import numpy as np 
import matplotlib.patches as mpatches 
import matplotlib.pyplot as plt 

df = pd.DataFrame(np.random.rand(100,1), columns=['Saving']) 
df['SKU'] = np.arange(100) 
df['label'] = np.random.choice(['a', 'b', 'c','d'], 100) 

fig, ax = plt.subplots() 
colors = {'a':'red', 'b':'blue', 'c':'green', 'd':'white'} 
figSaving = ax.scatter(df['SKU'], df['Saving'], c=df['label'].apply(lambda x: colors[x])) 


# build the legend 
red_patch = mpatches.Patch(color='red', label='a') 
blue_patch = mpatches.Patch(color='blue', label='b') 
green_patch = mpatches.Patch(color='green', label='c') 
white_patch = mpatches.Patch(color='white', label='d') 

# set up for handles declaration 
patches = [red_patch, blue_patch, green_patch, white_patch] 

# define and place the legend 
#legend = ax.legend(handles=patches,loc='upper right') 

# alternative declaration for placing legend outside of plot 
legend = ax.legend(handles=patches,bbox_to_anchor=(1.05, 1), loc=2, borderaxespad=0.) 

plt.show() 

Answer 2

plt.legend是可调用的。通过写plt.legend={'a', 'b', 'c', 'd'}，要更换调用由set，这本身并没有什么（除了使其无法事后打电话legend。你想要做的是调用plt.legend()见https://matplotlib.org/users/legend_guide.html。