如何在 Matplotlib 的散点图中添加图例？

在本文中，我们将使用matplotlib模块为描绘的图像添加图例。我们将使用matplotlib.pyplot.legend()方法来描述和标记图形的元素，并从同一图形中区分不同的图。

Syntax: matplotlib.pyplot.legend( [“title_1”, “Title_2”],  ncol = 1 , loc = “upper left” ,bbox_to_anchor =(1, 1) )

Parameters :

• ncol: [takes int, optional parameter] the default value is 1. It represents the number of columns in legend.
• loc: [takes string, optional parameter] the default value is “best” i.e “upper left”. It represents the location of the legend. Other options can be: “best”, “upper right”, “upper left”, “lower left”, “lower right” , “right”, “center left”, “center right”, “lower center”, “upper center”, “center”.
• bbox_to_anchor: [takes a list or tuple of 2 int/float, optional parameter ]. It represents the co-ordinates of legend on the graph. Both x and y co-ordinates are mandatory to give.

示例 1：

Python3

# import required modules
import matplotlib.pyplot as plt
  
# adjust coordinates
x =  [1,2,3,4,5]
y1 = [2,4,6,8,10]
y2 = [3,6,9,12,15]
  
# depict illustration
plt.scatter(x, y1)
plt.scatter(x,y2)
  
# apply legend()
plt.legend(["x*2" , "x*3"])
plt.show()

输出：

示例 2：

蟒蛇3

# impoert required modules
import matplotlib.pyplot as plt
  
# adjust coordinates
x =  [1,2,3,4,5]
y1 = [2,4,6,8,10]
y2 = [3,6,9,12,15]
  
# depict illustration
plt.scatter(x, y1)
plt.scatter(x,y2)
  
# appply legend()
plt.legend(["x*2" , "x*3"], ncol = 2 , loc = "lower right")
plt.show()

输出：

示例 3：

蟒蛇3

# import required modules
import matplotlib.pyplot as plt
  
# adjust coordinates
x =  [1,2,3,4,5]
y1 = [2,4,6,8,10]
y2 = [3,6,9,12,15]
  
# depict illustartion
plt.scatter(x, y1)
plt.scatter(x,y2)
  
# apply legend()
plt.legend(["x*2" , "x*3"], bbox_to_anchor = (1 , 1))
plt.show()

输出：

注意：我们可以使用“label”参数在 matplotlib.pyplot.scatter() 中标记绘图的元素。但是，要显示它，必须编写matplotlib.pyplot.legend() 。

示例 4：

蟒蛇3

# import required modules
import matplotlib.pyplot as plt
import numpy as np
  
# assign coordinates
x = np.arange(1, 6)
y1 = x**2
y2 = x**4
  
# depict illustration
plt.scatter(x, y1, label="x**2")
plt.scatter(x, y2, label="x**4")
  
# apply legend()
plt.legend()
plt.show()

输出：

注意：如果matplotlib.pyplot.legend()不是用代码编写的，那么标签将不会显示。