简单版本，按照李航的《统计学习方法》的思路编写

数据采用了著名的sklearn自带的iries数据，最优化求解采用了SGD算法。

预处理增加了标准化操作。

'''
perceptron classifier
 
created on 2019.9.14
author: vince
'''
import pandas
import numpy
import logging
import matplotlib.pyplot as plt
 
from sklearn.datasets import load_iris
from sklearn.model_selection import train_test_split
from sklearn.metrics import accuracy_score
 
'''
perceptron classifier
 
Attributes
w: ld-array = weights after training
l: list = number of misclassification during each iteration
'''
class Perceptron:
  def __init__(self,eta = 0.01,iter_num = 50,batch_size = 1):
    '''
    eta: float = learning rate (between 0.0 and 1.0).
    iter_num: int = iteration over the training dataset.
    batch_size: int = gradient descent batch number,if batch_size == 1,used SGD;
      if batch_size == 0,use BGD;
      else MBGD;
    '''
 
    self.eta = eta;
    self.iter_num = iter_num;
    self.batch_size = batch_size;
 
  def train(self,X,Y):
    '''
    train training data.
    X:{array-like},shape=[n_samples,n_features] = Training vectors,where n_samples is the number of training samples and
      n_features is the number of features.
    Y:{array-like},share=[n_samples] = traget values.
    '''
    self.w = numpy.zeros(1 + X.shape[1]);
    self.l = numpy.zeros(self.iter_num);
    for iter_index in range(self.iter_num):
      for sample_index in range(X.shape[0]):
        if (self.activation(X[sample_index]) != Y[sample_index]):
          logging.debug("%s: pred(%s),label(%s),%s,%s" % (sample_index,self.net_input(X[sample_index]),Y[sample_index],X[sample_index,0],1]));
          self.l[iter_index] += 1;
      for sample_index in range(X.shape[0]):
        if (self.activation(X[sample_index]) != Y[sample_index]):
          self.w[0] += self.eta * Y[sample_index];
          self.w[1:] += self.eta * numpy.dot(X[sample_index],Y[sample_index]);
          break;
      logging.info("iter %s: %s,%s" %
          (iter_index,self.w[0],self.w[1],self.w[2],self.l[iter_index]));
 
  def activation(self,x):
    return numpy.where(self.net_input(x) >= 0.0,1,-1);
 
  def net_input(self,x):
    return numpy.dot(x,self.w[1:]) + self.w[0];
 
  def predict(self,x):
    return self.activation(x);
 
def main():
  logging.basicConfig(level = logging.INFO,format = '%(asctime)s %(filename)s[line:%(lineno)d] %(levelname)s %(message)s',datefmt = '%a,%d %b %Y %H:%M:%S');
 
  iris = load_iris();
 
  features = iris.data[:99,[0,2]];
  # normalization
  features_std = numpy.copy(features);
  for i in range(features.shape[1]):
    features_std[:,i] = (features_std[:,i] - features[:,i].mean()) / features[:,i].std();
 
  labels = numpy.where(iris.target[:99] == 0,-1,1);
 
  # 2/3 data from training,1/3 data for testing
  train_features,test_features,train_labels,test_labels = train_test_split(
      features_std,labels,test_size = 0.33,random_state = 23323);
 
  logging.info("train set shape:%s" % (str(train_features.shape)));
 
  p = Perceptron();
 
  p.train(train_features,train_labels);
 
  test_predict = numpy.array([]);
  for feature in test_features:
    predict_label = p.predict(feature);
    test_predict = numpy.append(test_predict,predict_label);
 
  score = accuracy_score(test_labels,test_predict);
  logging.info("The accruacy score is: %s "% (str(score)));
 
  #plot
  x_min,x_max = train_features[:,0].min() - 1,train_features[:,0].max() + 1;
  y_min,y_max = train_features[:,1].min() - 1,1].max() + 1;
  plt.xlim(x_min,x_max);
  plt.ylim(y_min,y_max);
  plt.xlabel("width");
  plt.ylabel("heigt");
 
  plt.scatter(train_features[:,1],c = train_labels,marker = 'o',s = 10);
 
  k = - p.w[1] / p.w[2];
  d = - p.w[0] / p.w[2];
 
  plt.plot([x_min,x_max],[k * x_min + d,k * x_max + d],"go-");
 
  plt.show();
 
if __name__ == "__main__":
  main();

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