import matplotlib.pyplot as plt     #加载matplotlib用于数据的可视化
from sklearn.decomposition import PCA   #加载PCA算法包
from sklearn.datasets import load_iris


data=load_iris()
y=data.target
x=data.data
pca=PCA(n_components=2)  #加载PCA算法，设置降维后主成分数目为2
reduced_x=pca.fit_transform(x)#对样本进行降维

red_x,red_y=[],[]
blue_x,blue_y=[],[]
green_x,green_y=[],[]


for i in range(len(reduced_x)):
 if y[i] ==0:
  red_x.append(reduced_x[i][0])
  red_y.append(reduced_x[i][1])

 elif y[i]==1:
  blue_x.append(reduced_x[i][0])
  blue_y.append(reduced_x[i][1])

 else:
  green_x.append(reduced_x[i][0])
  green_y.append(reduced_x[i][1])

#可视化
plt.scatter(red_x,red_y,c='r',marker='x')
plt.scatter(blue_x,blue_y,c='b',marker='D')
plt.scatter(green_x,green_y,c='g',marker='.')
plt.show()

import matplotlib.pyplot as plt
import sklearn.decomposition as dp
from sklearn.datasets.base import load_iris

x,y=load_iris(return_X_y=True) #加载数据，x表示数据集中的属性数据，y表示数据标签
pca=dp.PCA(n_components=2) #加载pca算法，设置降维后主成分数目为2
reduced_x=pca.fit_transform(x) #对原始数据进行降维，保存在reduced_x中
red_x,red_y=[],[]
blue_x,blue_y=[],[]
green_x,green_y=[],[]
for i in range(len(reduced_x)): #按鸢尾花的类别将降维后的数据点保存在不同的表表中
 if y[i]==0:
  red_x.append(reduced_x[i][0])
  red_y.append(reduced_x[i][1])
 elif y[i]==1:
  blue_x.append(reduced_x[i][0])
  blue_y.append(reduced_x[i][1])
 else:
  green_x.append(reduced_x[i][0])
  green_y.append(reduced_x[i][1])
plt.scatter(red_x,red_y,c='r',marker='x')
plt.scatter(blue_x,blue_y,c='b',marker='D')
plt.scatter(green_x,green_y,c='g',marker='.')
plt.show()