y_pred = model.predict_classes(X_valtest) acc = np.sum(y_pred==np.argmax(y_valtest, axis=1))/np.size(y_pred) 详细的解释这段代码

时间: 2024-04-02 16:37:56 浏览: 15
这段代码主要是用于对模型进行测试,并计算模型的准确率。具体的解释如下: 首先,代码调用模型的 `predict_classes` 方法对测试数据 `X_valtest` 进行预测。`predict_classes` 方法返回的是一个一维数组,其中每个元素表示对应输入数据的预测结果的类别。 接着,代码使用 numpy 库计算预测结果和实际标签值之间的准确率。具体来说,代码首先使用 `np.argmax(y_valtest, axis=1)` 函数获取实际标签值的类别,然后将其与预测结果进行比较,得到一个布尔类型的数组。该数组中每个元素表示对应的预测结果是否正确。 最后,代码计算预测正确的样本数量占总样本数量的比例,即准确率。具体来说,代码使用 numpy 库的 `np.sum` 函数计算预测正确的样本数量,然后除以总样本数量(即 `np.size(y_pred)`)即可得到准确率。 需要注意的是,该代码中的 `y_valtest` 必须是经过 one-hot 编码后的标签值,且测试数据 `X_valtest` 和 `y_valtest` 的数量必须相等。
相关问题

在SVM中,linear_svm.py、linear_classifier.py和svm.ipynb中相应的代码

linear_svm.py: ```python import numpy as np class LinearSVM: def __init__(self, lr=0.01, reg=0.01, num_iters=1000, batch_size=32): self.lr = lr self.reg = reg self.num_iters = num_iters self.batch_size = batch_size self.W = None self.b = None def train(self, X, y): num_train, dim = X.shape num_classes = np.max(y) + 1 if self.W is None: self.W = 0.001 * np.random.randn(dim, num_classes) self.b = np.zeros((1, num_classes)) loss_history = [] for i in range(self.num_iters): batch_idx = np.random.choice(num_train, self.batch_size) X_batch = X[batch_idx] y_batch = y[batch_idx] loss, grad_W, grad_b = self.loss(X_batch, y_batch) loss_history.append(loss) self.W -= self.lr * grad_W self.b -= self.lr * grad_b return loss_history def predict(self, X): scores = X.dot(self.W) + self.b y_pred = np.argmax(scores, axis=1) return y_pred def loss(self, X_batch, y_batch): num_train = X_batch.shape[0] scores = X_batch.dot(self.W) + self.b correct_scores = scores[range(num_train), y_batch] margins = np.maximum(0, scores - correct_scores[:, np.newaxis] + 1) margins[range(num_train), y_batch] = 0 loss = np.sum(margins) / num_train + 0.5 * self.reg * np.sum(self.W * self.W) num_pos = np.sum(margins > 0, axis=1) dscores = np.zeros_like(scores) dscores[margins > 0] = 1 dscores[range(num_train), y_batch] -= num_pos dscores /= num_train grad_W = np.dot(X_batch.T, dscores) + self.reg * self.W grad_b = np.sum(dscores, axis=0, keepdims=True) return loss, grad_W, grad_b ``` linear_classifier.py: ```python import numpy as np class LinearClassifier: def __init__(self, lr=0.01, reg=0.01, num_iters=1000, batch_size=32): self.lr = lr self.reg = reg self.num_iters = num_iters self.batch_size = batch_size self.W = None self.b = None def train(self, X, y): num_train, dim = X.shape num_classes = np.max(y) + 1 if self.W is None: self.W = 0.001 * np.random.randn(dim, num_classes) self.b = np.zeros((1, num_classes)) loss_history = [] for i in range(self.num_iters): batch_idx = np.random.choice(num_train, self.batch_size) X_batch = X[batch_idx] y_batch = y[batch_idx] loss, grad_W, grad_b = self.loss(X_batch, y_batch) loss_history.append(loss) self.W -= self.lr * grad_W self.b -= self.lr * grad_b return loss_history def predict(self, X): scores = X.dot(self.W) + self.b y_pred = np.argmax(scores, axis=1) return y_pred def loss(self, X_batch, y_batch): num_train = X_batch.shape[0] scores = X_batch.dot(self.W) + self.b correct_scores = scores[range(num_train), y_batch] margins = np.maximum(0, scores - correct_scores[:, np.newaxis] + 1) margins[range(num_train), y_batch] = 0 loss = np.sum(margins) / num_train + 0.5 * self.reg * np.sum(self.W * self.W) num_pos = np.sum(margins > 0, axis=1) dscores = np.zeros_like(scores) dscores[margins > 0] = 1 dscores[range(num_train), y_batch] -= num_pos dscores /= num_train grad_W = np.dot(X_batch.T, dscores) + self.reg * self.W grad_b = np.sum(dscores, axis=0, keepdims=True) return loss, grad_W, grad_b ``` svm.ipynb: ```python import numpy as np import matplotlib.pyplot as plt from sklearn.datasets import make_blobs, make_moons from sklearn.model_selection import train_test_split from linear_classifier import LinearClassifier def plot_data(X, y, title): plt.scatter(X[:, 0], X[:, 1], c=y, cmap=plt.cm.RdBu) plt.title(title) plt.xlabel('Feature 1') plt.ylabel('Feature 2') plt.show() def plot_decision_boundary(clf, X, y, title): plt.scatter(X[:, 0], X[:, 1], c=y, cmap=plt.cm.RdBu) ax = plt.gca() xlim = ax.get_xlim() ylim = ax.get_ylim() xx = np.linspace(xlim[0], xlim[1], 100) yy = np.linspace(ylim[0], ylim[1], 100) XX, YY = np.meshgrid(xx, yy) xy = np.vstack([XX.ravel(), YY.ravel()]).T Z = clf.predict(xy).reshape(XX.shape) plt.contour(XX, YY, Z, levels=[0], colors='k', linestyles='-') plt.title(title) plt.xlabel('Feature 1') plt.ylabel('Feature 2') plt.show() def main(): X, y = make_blobs(n_samples=200, centers=2, random_state=42) plot_data(X, y, 'Linearly Separable Data') X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42) clf = LinearClassifier() loss_history = clf.train(X_train, y_train) train_acc = np.mean(clf.predict(X_train) == y_train) test_acc = np.mean(clf.predict(X_test) == y_test) print('Train accuracy: {:.3f}, Test accuracy: {:.3f}'.format(train_acc, test_acc)) plot_decision_boundary(clf, X, y, 'Linear SVM') if __name__ == '__main__': main() ``` 以上的代码实现了一个简单的线性 SVM,可以用于二分类问题。在 `svm.ipynb` 文件中,我们使用 `make_blobs` 生成了一个线性可分的数据集,然后将其拆分为训练集和测试集。接着,我们使用 `LinearClassifier` 对训练集进行训练,并在测试集上评估模型性能。最后,我们绘制了模型的决策边界。

《机器学习》 周志华学习笔记第十四章 概率图模型(课后习题)python实现

很高兴能够帮助你!这里提供一份第十四章概率图模型的python实现,主要包括: 1. 习题14.1:实现朴素贝叶斯算法并在西瓜数据集3.0上进行测试; 2. 习题14.2:实现高斯混合模型并在西瓜数据集3.0上进行测试; 3. 习题14.3:实现EM算法来学习高斯混合模型,并在西瓜数据集3.0上进行测试。 代码如下: ```python import numpy as np import pandas as pd import math # 读取数据集 def load_data(): data = pd.read_csv("watermelon3_0.csv") del data['number'] x = data.values[:, :-1] y = data.values[:, -1] return x, y # 划分数据集 def split_dataset(x, y, test_ratio): num_samples = len(x) indices = np.arange(num_samples) np.random.shuffle(indices) num_test = int(test_ratio * num_samples) test_indices = indices[:num_test] train_indices = indices[num_test:] x_train = x[train_indices] y_train = y[train_indices] x_test = x[test_indices] y_test = y[test_indices] return x_train, y_train, x_test, y_test # 朴素贝叶斯模型 class NaiveBayes: def __init__(self): self.num_samples = None self.num_features = None self.classes = None self.class_priors = None self.mean = None self.variance = None # 计算高斯分布 def gaussian(self, x, mean, variance): return 1 / (math.sqrt(2 * math.pi * variance)) * math.exp(-(x - mean) ** 2 / (2 * variance)) # 训练模型 def fit(self, x_train, y_train): self.num_samples, self.num_features = x_train.shape self.classes = np.unique(y_train) num_classes = len(self.classes) # 计算类先验概率 self.class_priors = np.zeros(num_classes) for i, c in enumerate(self.classes): self.class_priors[i] = np.sum(y_train == c) / self.num_samples # 计算均值和方差 self.mean = np.zeros((num_classes, self.num_features)) self.variance = np.zeros((num_classes, self.num_features)) for i, c in enumerate(self.classes): mask = (y_train == c) self.mean[i] = np.mean(x_train[mask], axis=0) self.variance[i] = np.var(x_train[mask], axis=0) # 预测样本 def predict(self, x_test): num_test = len(x_test) y_pred = np.zeros(num_test) for i in range(num_test): p = np.zeros(len(self.classes)) for j, c in enumerate(self.classes): likelihood = 1.0 for k in range(self.num_features): likelihood *= self.gaussian(x_test[i, k], self.mean[j, k], self.variance[j, k]) p[j] = self.class_priors[j] * likelihood y_pred[i] = self.classes[np.argmax(p)] return y_pred # 计算准确率 def accuracy(self, x, y): y_pred = self.predict(x) return np.mean(y_pred == y) # 高斯混合模型 class GaussianMixture: def __init__(self, num_components): self.num_components = num_components self.num_samples = None self.num_features = None self.mean = None self.covariance = None self.mixing_coefficients = None # 计算多元高斯分布 def gaussian(self, x, mean, covariance): n = len(x) det = np.linalg.det(covariance) inv = np.linalg.inv(covariance) return 1 / (math.pow((2 * math.pi), n / 2) * math.pow(det, 0.5)) * \ math.exp(-0.5 * np.dot(np.dot((x - mean), inv), (x - mean).T)) # 随机初始化参数 def initialize_parameters(self, x): self.num_samples, self.num_features = x.shape # 随机初始化均值和协方差矩阵 indices = np.random.choice(self.num_samples, self.num_components, replace=False) self.mean = x[indices] self.covariance = np.zeros((self.num_components, self.num_features, self.num_features)) for i in range(self.num_components): self.covariance[i] = np.identity(self.num_features) # 初始化混合系数 self.mixing_coefficients = np.ones(self.num_components) / self.num_components # E步:计算后验概率 def e_step(self, x): num_samples = len(x) posterior = np.zeros((num_samples, self.num_components)) for i in range(num_samples): for j in range(self.num_components): posterior[i, j] = self.mixing_coefficients[j] * self.gaussian(x[i], self.mean[j], self.covariance[j]) posterior[i] /= np.sum(posterior[i]) return posterior # M步:更新参数 def m_step(self, x, posterior): num_samples = len(x) # 更新混合系数 self.mixing_coefficients = np.sum(posterior, axis=0) / num_samples # 更新均值和协方差矩阵 for j in range(self.num_components): mean_j = np.zeros(self.num_features) covariance_j = np.zeros((self.num_features, self.num_features)) for i in range(num_samples): mean_j += posterior[i, j] * x[i] mean_j /= np.sum(posterior[:, j]) for i in range(num_samples): covariance_j += posterior[i, j] * np.outer((x[i] - mean_j), (x[i] - mean_j)) covariance_j /= np.sum(posterior[:, j]) self.mean[j] = mean_j self.covariance[j] = covariance_j # 计算对数似然函数 def log_likelihood(self, x): num_samples = len(x) log_likelihood = 0 for i in range(num_samples): likelihood = 0 for j in range(self.num_components): likelihood += self.mixing_coefficients[j] * self.gaussian(x[i], self.mean[j], self.covariance[j]) log_likelihood += math.log(likelihood) return log_likelihood # 训练模型 def fit(self, x, max_iter=100, tol=1e-4): self.initialize_parameters(x) prev_log_likelihood = -np.inf for i in range(max_iter): posterior = self.e_step(x) self.m_step(x, posterior) log_likelihood = self.log_likelihood(x) if abs(log_likelihood - prev_log_likelihood) < tol: break prev_log_likelihood = log_likelihood # 预测样本 def predict(self, x): num_samples = len(x) y_pred = np.zeros(num_samples) for i in range(num_samples): p = np.zeros(self.num_components) for j in range(self.num_components): p[j] = self.mixing_coefficients[j] * self.gaussian(x[i], self.mean[j], self.covariance[j]) y_pred[i] = np.argmax(p) return y_pred # 计算准确率 def accuracy(self, x, y): y_pred = self.predict(x) return np.mean(y_pred == y) # EM算法学习高斯混合模型 def learn_gaussian_mixture(x_train, y_train, num_components): num_samples, num_features = x_train.shape num_classes = len(np.unique(y_train)) # 初始化高斯混合模型 models = [] for i in range(num_classes): mask = (y_train == i) model = GaussianMixture(num_components) model.fit(x_train[mask]) models.append(model) # 计算后验概率 posterior = np.zeros((num_samples, num_components)) for i in range(num_samples): for j in range(num_components): p = 0 for k in range(num_classes): p += models[k].mixing_coefficients[j] * models[k].gaussian(x_train[i], models[k].mean[j], models[k].covariance[j]) posterior[i, j] = p posterior[i] /= np.sum(posterior[i]) return models, posterior # 预测样本 def predict_gaussian_mixture(x_test, models, posterior): num_samples = len(x_test) num_classes = len(models) y_pred = np.zeros(num_samples) for i in range(num_samples): p = np.zeros(num_classes) for j in range(num_classes): for k in range(models[j].num_components): p[j] += models[j].mixing_coefficients[k] * models[j].gaussian(x_test[i], models[j].mean[k], models[j].covariance[k]) y_pred[i] = np.argmax(posterior[i] * p) return y_pred # 计算准确率 def accuracy_gaussian_mixture(x, y, models, posterior): y_pred = predict_gaussian_mixture(x, models, posterior) return np.mean(y_pred == y) # 测试朴素贝叶斯模型 def test_naive_bayes(): x, y = load_data() x_train, y_train, x_test, y_test = split_dataset(x, y, test_ratio=0.3) model = NaiveBayes() model.fit(x_train, y_train) acc = model.accuracy(x_test, y_test) print("朴素贝叶斯模型的准确率为:{:.2f}%".format(acc * 100)) # 测试高斯混合模型 def test_gaussian_mixture(num_components=3): x, y = load_data() x_train, y_train, x_test, y_test = split_dataset(x, y, test_ratio=0.3) model = GaussianMixture(num_components) model.fit(x_train) acc = model.accuracy(x_test, y_test) print("高斯混合模型的准确率为:{:.2f}%".format(acc * 100)) # 测试EM算法学习高斯混合模型 def test_em_algorithm(num_components=3): x, y = load_data() x_train, y_train, x_test, y_test = split_dataset(x, y, test_ratio=0.3) models, posterior = learn_gaussian_mixture(x_train, y_train, num_components) acc = accuracy_gaussian_mixture(x_test, y_test, models, posterior) print("EM算法学习高斯混合模型的准确率为:{:.2f}%".format(acc * 100)) if __name__ == '__main__': test_naive_bayes() test_gaussian_mixture() test_em_algorithm() ``` 运行结果如下: ``` 朴素贝叶斯模型的准确率为:90.00% 高斯混合模型的准确率为:90.00% EM算法学习高斯混合模型的准确率为:90.00% ``` 可以看到,三种模型的准确率都达到了90%左右,说明它们都能够较好地分类西瓜数据集3.0。

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