matplotlib直方图与图例

Question

我有这段代码产生一个直方图，标识三种类型的字段; “低”， “中等” 和 “高”：

import pylab as plt 
import pandas as pd 


df = pd.read_csv('April2017NEW.csv', index_col =1) 
df1 = df.loc['Output Energy, (Wh/h)'] # choose index value and Average 
df1['Average'] = df1.mean(axis=1) 

N, bins, patches = plt.hist(df1['Average'], 30) 

cmap = plt.get_cmap('jet') 
low = cmap(0.5) 
medium =cmap(0.25) 
high = cmap(0.8) 


for i in range(0,4): 
    patches[i].set_facecolor(low) 
for i in range(4,11): 
    patches[i].set_facecolor(medium) 
for i in range(11,30): 
    patches[i].set_facecolor(high) 

plt.xlabel("Watt Hours", fontsize=16) 
plt.ylabel("Households", fontsize=16) 
plt.xticks(fontsize=14) 
plt.yticks(fontsize=14) 
ax = plt.subplot(111) 
ax.spines["top"].set_visible(False) 
ax.spines["right"].set_visible(False) 

plt.show() 

产生这样的：

如何获得一个传说中有三个不同的颜色？

Answer 1

您需要自己创建图例。为此，创建一些矩形，图中未显示（所谓的代理艺术家）。

#create legend 
handles = [Rectangle((0,0),1,1,color=c,ec="k") for c in [low,medium, high]] 
labels= ["low","medium", "high"] 
plt.legend(handles, labels) 

完整示例：

import matplotlib.pyplot as plt 
import numpy as np 
from matplotlib.patches import Rectangle 

data = np.random.rayleigh(size=1000)*35 

N, bins, patches = plt.hist(data, 30, ec="k") 

cmap = plt.get_cmap('jet') 
low = cmap(0.5) 
medium =cmap(0.25) 
high = cmap(0.8) 


for i in range(0,4): 
    patches[i].set_facecolor(low) 
for i in range(4,11): 
    patches[i].set_facecolor(medium) 
for i in range(11,30): 
    patches[i].set_facecolor(high) 

#create legend 
handles = [Rectangle((0,0),1,1,color=c,ec="k") for c in [low,medium, high]] 
labels= ["low","medium", "high"] 
plt.legend(handles, labels) 

plt.xlabel("Watt Hours", fontsize=16) 
plt.ylabel("Households", fontsize=16) 
plt.xticks(fontsize=14) 
plt.yticks(fontsize=14) 

plt.gca().spines["top"].set_visible(False) 
plt.gca().spines["right"].set_visible(False) 

plt.show()