python - 如何向 matplotlib 散点图添加图例

Question

我正在尝试绘制 PCA，其中一种颜色是标签 1，另一种颜色应该是标签 2。当我想添加带有 ax1.legend() 的图例时我只得到蓝点的标签或根本没有标签。如何为蓝色和紫色点添加带有正确标签的图例？

sns.set(style = 'darkgrid')

fig, ax1 = sns.plt.subplots()  

x1, x2 = X_bar[:,0], X_bar[:,1] 
ax1.scatter(x1, x2, 100, edgecolors='none', c = colors)
fig.set_figheight(8)
fig.set_figwidth(15)

Answer 1

看起来您正在绘制在两种颜色之间振荡的每个点。根据这个问题的答案subsampling every nth entry in a numpy array您可以使用 numpys 数组切片来绘制两个单独的数组，然后照常执行图例。
对于一些示例数据:

import numpy as np
import numpy.random as nprnd
import matplotlib.pyplot as plt

A = nprnd.randint(1000, size=100)
A.shape = (50,2)

x1, x2 = np.sort(A[:,0], axis=0), np.sort(A[:,1], axis=0)

x1
Out[50]: 
array([ 46,  63,  84,  96, 118, 127, 137, 142, 181, 187, 187, 207, 210,
       238, 238, 330, 334, 335, 346, 346, 350, 392, 400, 426, 467, 531,
       550, 567, 569, 572, 583, 625, 637, 661, 671, 677, 698, 713, 777,
       796, 837, 850, 866, 868, 874, 890, 919, 972, 992, 993])
x2
Out[51]: 
array([  2,  44,  49,  51,  72,  84,  86, 118, 120, 133, 150, 155, 156,
       159, 199, 202, 250, 281, 289, 317, 317, 386, 405, 414, 427, 461,
       507, 510, 543, 552, 553, 555, 559, 576, 618, 622, 633, 647, 665,
       672, 682, 685, 745, 767, 776, 802, 808, 813, 847, 973])


labels=['blue','red']

fig, ax1 = plt.subplots()
ax1.scatter(x1[0::2], x2[0::2], 100, edgecolors='none', c='red', label = 'red')
ax1.scatter(x1[1::2], x2[1::2], 100, edgecolors='none', c='black', label = 'black')

plt.legend()
plt.show()

对于您的代码，您可以执行以下操作:

sns.set(style = 'darkgrid')
fig, ax1 = sns.plt.subplots()  

x1, x2 = X_bar[:,0], X_bar[:,1] 
ax1.scatter(x1[0::2], x2[0::2], 100, edgecolors='none', c = colors[0], label='one')
ax1.scatter(x1[1::2], x2[1::2], 100, edgecolors='none', c = colors[1], label='two')
fig.set_figheight(8)
fig.set_figwidth(15)
plt.legend()