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。