import numpy as np import matplotlib.pyplot as plt from matplotlib.colors import ListedColormap from sklearn import neighbors, datasets n_neighbors = 15 iris = datasets.load_iris() X = iris.data[:, :2] y = iris.target h = .02 # step size in the mesh cmap_light = ListedColormap(['#FFAAAA', '#AAFFAA', '#AAAAFF']) cmap_bold = ListedColormap(['#FF0000', '#00FF00', '#0000FF']) weights = 'distance' clf = neighbors.KNeighborsClassifier(n_neighbors, weights)() clf.fit(X, y) x_min, x_max = X[:, 0].min() - 1, X[:, 0].max() + 1 y_min, y_max = X[:, 1].min() - 1, X[:, 1].max() + 1 xx, yy = np.meshgrid(np.arange(x_min, x_max, h),np.arange(y_min, y_max, h)) Z = clf.predict(np.c_[xx.ravel(), yy.ravel()]) Z = Z.reshape(xx.shape) plt.figure() plt.pcolormesh(xx, yy, Z, cmap=cmap_light) plt.scatter(X[:, 0], X[:, 1], c=y, cmap=cmap_bold, edgecolor='k', s=20) plt.xlim(xx.min(), xx.max()) plt.ylim(yy.min(), yy.max()) plt.title("3-Class classification (k = %i, weights = '%s')"% (n_neighbors,weights)) plt.show()

这段代码是一个示例，演示了如何使用 k-最近邻算法进行三类别的分类，并使用 matplotlib 绘制分类结果的决策边界和数据点。

首先，导入必要的库，包括 numpy、matplotlib 和 sklearn。然后，设置了一些参数，如 k 值、数据集（这里使用的是鸢尾花数据集）以及步长 h。接下来，定义了两个颜色映射，用于可视化分类结果。

然后，创建了一个 KNeighborsClassifier 对象 clf，传入了 k 值和权重参数。调用 fit() 方法拟合模型，传入特征数据 X 和标签数据 y。

接着，计算了决策边界的网格点坐标，并使用 predict() 方法对网格点进行预测，得到预测结果 Z。最后，将预测结果 Z 重塑为与网格点坐标相同的形状。

最后，使用 matplotlib 绘制了分类结果的决策边界和数据点。pcolormesh() 函数用于绘制决策边界的背景颜色，scatter() 函数用于绘制数据点。设置了坐标轴范围、标题等，并调用 show() 函数显示图形。

相关问题

在Python中想运行from sklearn.model_selection import train_test_split from sklearn.decomposition import PCA import pandas as pd from sklearn import svm import numpy as np import math import matplotlib.pyplot as plt import matplotlib as mpl from matplotlib import colors from sklearn.model_selection import train_test_split from sklearn import datasets from matplotlib.colors import ListedColormap from sklearn.svm import SVC from sklearn.preprocessing import StandardScaler from sklearn.model_selection import StratifiedShuffleSplit,StratifiedKFold from sklearn.model_selection import GridSearchCV from sklearn.model_selection import GridSearchCV, LeaveOneOut, cross_val_predict from sklearn.model_selection import KFold from sklearn.linear_model import LogisticRegression from sklearn.naive_bayes import GaussianNB from sklearn.neighbors import KNeighborsClassifier from sklearn import svm from sklearn.tree import DecisionTreeClassifier from sklearn.ensemble import RandomForestClassifier from sklearn.metrics import roc_auc_score from sklearn.metrics import roc_auc_score import math import datetime import multiprocessing as mp from sklearn.ensemble import StackingClassifier from sklearn.pipeline import make_pipeline from sklearn.svm import LinearSVC import random怎么操作

要在Python中运行这些代码，你需要确保已经安装了相应的包。大多数包都可以使用`pip`进行安装。

首先，在命令行中运行以下命令来安装所需的包：

pip install scikit-learn pandas matplotlib numpy

然后，在你的Python脚本中导入所需的库：

from sklearn.model_selection import train_test_split
from sklearn.decomposition import PCA
import pandas as pd
from sklearn import svm
import numpy as np
import math
import matplotlib.pyplot as plt
import matplotlib as mpl
from matplotlib import colors
from sklearn.model_selection import train_test_split
from sklearn import datasets
from matplotlib.colors import ListedColormap
from sklearn.svm import SVC
from sklearn.preprocessing import StandardScaler
from sklearn.model_selection import StratifiedShuffleSplit, StratifiedKFold
from sklearn.model_selection import GridSearchCV
from sklearn.model_selection import GridSearchCV, LeaveOneOut, cross_val_predict
from sklearn.model_selection import KFold
from sklearn.linear_model import LogisticRegression
from sklearn.naive_bayes import GaussianNB
from sklearn.neighbors import KNeighborsClassifier
from sklearn.tree import DecisionTreeClassifier
from sklearn.ensemble import RandomForestClassifier
from sklearn.metrics import roc_auc_score
import datetime
import multiprocessing as mp
from sklearn.ensemble import StackingClassifier
from sklearn.pipeline import make_pipeline
from sklearn.svm import LinearSVC

import random

请确保在运行这些代码之前，已经安装了所需的Python库。如果遇到任何问题，请确保已正确安装这些库，并且版本与代码兼容。

import numpy as np import matplotlib.pyplot as plt from matplotlib.colors import ListedColormap from sklearn.neighbors import KNeighborsClassifier from sklearn.datasets import load_iris iris=load_iris() X=iris.data[:,:2] Y=iris.target print(iris.feature_names) cmap_light=ListedColormap(['#FFAAAA','#AAFFAA','#AAAAFF']) cmap_bold=ListedColormap(['#FF0000','#00FF00','#0000FF']) clf=KNeighborsClassifier(n_neighbors=10,weights='uniform') clf.fit(X,Y) #画出决策边界 x_min,x_max=X[:,0].min()-1,X[:,0].max()+1 y_min,y_max=X[:,1].min()-1,X[:,1].max()+1 xx,yy=np.meshgrid(np.arange(x_min,x_max,0.02), np.arange(y_min,y_max,0.02)) Z=clf.predict(np.c_[xx.ravel(),yy.ravel()]) reshape(xx.shape) plt.figure() plt.pcolormesh(xx,yy,Z,cmap=cmap_light) #绘制预测结果图 plt.scatter(X[:,0],X[:,1],c=Y,cmap=cmap_bold) plt.xlim(xx,min(),xx.max()) plt.ylim(yy.min(),yy.max()) plt.title('3_Class(k=10,weights=uniform)') plt.show()

这段代码的作用是使用K近邻算法对鸢尾花数据集进行分类，并绘制出分类的决策边界图。具体来说，代码首先加载鸢尾花数据集并提取其中的前两个特征作为模型输入，然后使用KNeighborsClassifier类创建一个K近邻分类器，并使用fit方法拟合数据集。接着，代码使用meshgrid函数生成一组网格点，并将其作为输入数据进行分类预测，最后将分类结果绘制成彩色的决策边界图。同时，代码还会将数据集中的样本点用散点图表示出来。