adaboost算法Python完整实现
时间: 2023-11-03 18:17:05 浏览: 146
好的,这里是adaboost算法的Python完整实现:
```python
import numpy as np
class Adaboost:
def __init__(self, n_estimators=50, learning_rate=1.0):
self.n_estimators = n_estimators
self.learning_rate = learning_rate
self.models = []
self.alphas = []
def fit(self, X, y):
n_samples, n_features = X.shape
weights = np.full(n_samples, 1/n_samples)
for i in range(self.n_estimators):
model = DecisionTreeClassifier(max_depth=1)
model.fit(X, y, sample_weight=weights)
predictions = model.predict(X)
error = np.sum(weights * (predictions != y))
alpha = self.learning_rate * (np.log((1 - error) / error) + np.log(n_classes - 1))
weights *= np.exp(-alpha * y * predictions)
weights /= np.sum(weights)
self.models.append(model)
self.alphas.append(alpha)
def predict(self, X):
predictions = np.zeros(len(X))
for alpha, model in zip(self.alphas, self.models):
predictions += alpha * model.predict(X)
return np.sign(predictions)
```
这里我们使用了 `DecisionTreeClassifier` 作为基分类器,当然也可以使用其他的分类器。在 `fit` 函数中进行了 `n_estimators` 次迭代,每次迭代中训练一个基分类器,计算其预测结果与真实值之间的误差,然后计算其对应的权重 `alpha`,并更新样本权重,最后将训练好的基分类器和对应的权重存储起来。在预测时,我们根据每个基分类器的权重进行加权预测,并将结果取符号函数得到最终的预测结果。
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