机器学习编程作业（exe6）总结

r囧r小猫 2022-05-17 04:15 167阅读 0赞

在本练习的前半部分，您将使用具有各种示例2D数据集的支持向量机（SVM）。 对这些数据集进行实验将有助于您直观地了解SVM如何工作以及如何在SVM中使用高斯核函数。   
作业所提供的脚本ex6.m将帮助您逐步完成练习的前半部分。

%% Initialization
    clear ; close all; clc
    
    %% =============== Part 1: Loading and Visualizing Data ================
    %  We start the exercise by first loading and visualizing the dataset. 
    %  The following code will load the dataset into your environment and plot
    %  the data.
    %
    
    fprintf('Loading and Visualizing Data ...\n')
    
    % Load from ex6data1: 
    % You will have X, y in your environment
    load('ex6data1.mat');
    
    % Plot training data
    plotData(X, y);
    
    fprintf('Program paused. Press enter to continue.\n');
    pause;

%% ==================== Part 2: Training Linear SVM ====================
    %  The following code will train a linear SVM on the dataset and plot the
    %  decision boundary learned.
    %
    
    % Load from ex6data1: 
    % You will have X, y in your environment
    load('ex6data1.mat');
    
    fprintf('\nTraining Linear SVM ...\n')
    
    % You should try to change the C value below and see how the decision
    % boundary varies (e.g., try C = 1000)
    C = 100;% 这里进行更改来查看C的影响
    model = svmTrain(X, y, C, @linearKernel, 1e-3, 20);
    visualizeBoundaryLinear(X, y, model);
    
    fprintf('Program paused. Press enter to continue.\n');
    pause;

%% =============== Part 3: Implementing Gaussian Kernel ===============
    %  You will now implement the Gaussian kernel to use
    %  with the SVM. You should complete the code in gaussianKernel.m
    %
    fprintf('\nEvaluating the Gaussian Kernel ...\n')
    
    x1 = [1 2 1]; x2 = [0 4 -1]; sigma = 2;
    sim = gaussianKernel(x1, x2, sigma);
    
    fprintf(['Gaussian Kernel between x1 = [1; 2; 1], x2 = [0; 4; -1], sigma = %f :' ...
             '\n\t%f\n(for sigma = 2, this value should be about 0.324652)\n'], sigma, sim);
    
    fprintf('Program paused. Press enter to continue.\n');
    pause;

function sim = gaussianKernel(x1, x2, sigma)
    %RBFKERNEL returns a radial basis function kernel between x1 and x2
    %   sim = gaussianKernel(x1, x2) returns a gaussian kernel between x1 and x2
    %   and returns the value in sim
    
    % Ensure that x1 and x2 are column vectors
    x1 = x1(:); x2 = x2(:);
    
    % You need to return the following variables correctly.
    sim = 0;
    
    % ====================== YOUR CODE HERE ======================
    % Instructions: Fill in this function to return the similarity between x1
    %               and x2 computed using a Gaussian kernel with bandwidth
    %               sigma
    %
    % 高斯核函数定义
    sim = exp(-sum( (x1 - x2).^2) / ( 2 * (sigma.^2) ))
    % =============================================================
        
    end

%% =============== Part 4: Visualizing Dataset 2 ================
    %  The following code will load the next dataset into your environment and 
    %  plot the data. 
    %
    
    fprintf('Loading and Visualizing Data ...\n')
    
    % Load from ex6data2: 
    % You will have X, y in your environment
    load('ex6data2.mat');
    
    % Plot training data
    plotData(X, y);
    
    fprintf('Program paused. Press enter to continue.\n');
    pause;
    
    %% ========== Part 5: Training SVM with RBF Kernel (Dataset 2) ==========
    %  After you have implemented the kernel, we can now use it to train the 
    %  SVM classifier.
    % 
    fprintf('\nTraining SVM with RBF Kernel (this may take 1 to 2 minutes) ...\n');
    
    % Load from ex6data2: 
    % You will have X, y in your environment
    load('ex6data2.mat');
    
    % SVM Parameters
    C = 1; sigma = 0.1;
    
    % We set the tolerance and max_passes lower here so that the code will run
    % faster. However, in practice, you will want to run the training to
    % convergence.
    model= svmTrain(X, y, C, @(x1, x2) gaussianKernel(x1, x2, sigma)); 
    visualizeBoundary(X, y, model);
    
    fprintf('Program paused. Press enter to continue.\n');
    pause;

%% =============== Part 6: Visualizing Dataset 3 ================
    %  The following code will load the next dataset into your environment and 
    %  plot the data. 
    %
    
    fprintf('Loading and Visualizing Data ...\n')
    
    % Load from ex6data3: 
    % You will have X, y in your environment
    load('ex6data3.mat');
    
    % Plot training data
    plotData(X, y);
    
    fprintf('Program paused. Press enter to continue.\n');
    pause;

%% ========== Part 7: Training SVM with RBF Kernel (Dataset 3) ==========
    
    %  This is a different dataset that you can use to experiment with. Try
    %  different values of C and sigma here.
    % 
    
    % Load from ex6data3: 
    % You will have X, y in your environment
    load('ex6data3.mat');
    
    % Try different SVM Parameters here  
    % 通过SVM训练得出模型model，然后根据误差来选定最合适的C 和sigma
    [C, sigma] = dataset3Params(X, y, Xval, yval);
    
    % Train the SVM
    % 利用上面训练中得到的C, sigma来重新建立SVM模型
    model= svmTrain(X, y, C, @(x1, x2) gaussianKernel(x1, x2, sigma));
    visualizeBoundary(X, y, model);
    
    fprintf('Program paused. Press enter to continue.\n');
    pause;

**第二部分练习**

在下半部分的练习中，您将使用支持向量机来构建垃圾邮件分类器。

今天的许多电子邮件服务都提供了垃圾邮件过滤器，可以将电子邮件以高精度分类为垃圾邮件和非垃圾邮件。 在这部分练习中，您将使用SVM构建您自己的垃圾邮件过滤器。 您将会训练一个分类器来分类给定的电子邮件x是垃圾邮件（y = 1）还是非垃圾邮件（y = 0）。 特别是，您需要将每个电子邮件转换为一个特征向量x∈R n。 练习的以下部分将引导您如何通过电子邮件构建这样的特征向量。

在本练习的其余部分中，您将使用脚本ex6 spam.m. 本练习包含的数据集基于SpamAssassin公共语料库的一个子集。   
为了本练习的目的，您只能使用电子邮件正文（不包括电子邮件标题）。

function word_indices = processEmail(email_contents)
    %PROCESSEMAIL preprocesses a the body of an email and
    %returns a list of word_indices 
    %   word_indices = PROCESSEMAIL(email_contents) preprocesses 
    %   the body of an email and returns a list of indices of the 
    %   words contained in the email. 
    %
    
    % Load Vocabulary
    vocabList = getVocabList();
    
    % Init return value
    word_indices = [];
    
    % ========================== Preprocess Email ===========================
    
    % Find the Headers ( \n\n and remove )
    % Uncomment the following lines if you are working with raw emails with the
    % full headers
    
    % hdrstart = strfind(email_contents, ([char(10) char(10)]));
    % email_contents = email_contents(hdrstart(1):end);
    
    % Lower case  所有字母转成小写
    email_contents = lower(email_contents);
    
    % Strip all HTML
    % 移除HTML：所有的HTML标签都从电子邮件中删除
    % 许多电子邮件通常都带有HTML格式：我们删除所有的HTML标记，这样只有内容保留了。
    % Looks for any expression that starts with < and ends with > and replace
    % and does not have any < or > in the tag it with a space
    email_contents = regexprep(email_contents, '<[^<>]+>', ' ');
    
    % Handle Numbers 所有数字转成文本数字
    % Look for one or more characters between 0-9
    email_contents = regexprep(email_contents, '[0-9]+', 'number');
    
    % Handle URLS 处理掉网址链接
    % Look for strings starting with http:// or https://
    email_contents = regexprep(email_contents, ...
                               '(http|https)://[^\s]*', 'httpaddr');
    
    % Handle Email Addresses 处理掉邮箱
    % Look for strings with @ in the middle
    email_contents = regexprep(email_contents, '[^\s]+@[^\s]+', 'emailaddr');
    
    % Handle $ sign  处理掉美元符号
    email_contents = regexprep(email_contents, '[$]+', 'dollar');
    
    
    % ========================== Tokenize Email ===========================
    
    % Output the email to screen as well
    fprintf('\n==== Processed Email ====\n\n');
    
    % Process file
    l = 0;
    
    while ~isempty(email_contents)
    
        % Tokenize and also get rid of any punctuation
        [str, email_contents] = ...
           strtok(email_contents, ...
                  [' @$/#.-:&*+=[]?!(){},''">_<;%' char(10) char(13)]);
       
        % Remove any non alphanumeric characters
        str = regexprep(str, '[^a-zA-Z0-9]', '');
    
        % Stem the word 
        % (the porterStemmer sometimes has issues, so we use a try catch block)
        try str = porterStemmer(strtrim(str)); 
        catch str = ''; continue;
        end;
    
        % Skip the word if it is too short
        if length(str) < 1
           continue;
        end
    
        % Look up the word in the dictionary and add to word_indices if
        % found
        % ====================== YOUR CODE HERE ======================
        % Instructions: Fill in this function to add the index of str to
        %               word_indices if it is in the vocabulary. At this point
        %               of the code, you have a stemmed word from the email in
        %               the variable str. You should look up str in the
        %               vocabulary list (vocabList). If a match exists, you
        %               should add the index of the word to the word_indices
        %               vector. Concretely, if str = 'action', then you should
        %               look up the vocabulary list to find where in vocabList
        %               'action' appears. For example, if vocabList{18} =
        %               'action', then, you should add 18 to the word_indices 
        %               vector (e.g., word_indices = [word_indices ; 18]; ).
        % 
        % Note: vocabList{idx} returns a the word with index idx in the
        %       vocabulary list.
        % 
        % Note: You can use strcmp(str1, str2) to compare two strings (str1 and
        %       str2). It will return 1 only if the two strings are equivalent.
        %
        for i=1:length(vocabList)
             if strcmp(vocabList{i},str)==1
               word_indices = [word_indices ; i];
              end;
            end;  
        % =============================================================
        % Print to screen, ensuring that the output lines are not too long
        if (l + length(str) + 1) > 78
            fprintf('\n');
            l = 0;
        end
        fprintf('%s ', str);
        l = l + length(str) + 1;
    
    end
    
    % Print footer
    fprintf('\n\n=========================\n');
    
    end

function x = emailFeatures(word_indices)
    %EMAILFEATURES takes in a word_indices vector and produces a feature vector
    %from the word indices
    %   x = EMAILFEATURES(word_indices) takes in a word_indices vector and 
    %   produces a feature vector from the word indices. 
    
    % Total number of words in the dictionary
    n = 1899;
    
    % You need to return the following variables correctly.
    x = zeros(n, 1);
    
    % ====================== YOUR CODE HERE ======================
    % Instructions: Fill in this function to return a feature vector for the
    %               given email (word_indices). To help make it easier to 
    %               process the emails, we have have already pre-processed each
    %               email and converted each word in the email into an index in
    %               a fixed dictionary (of 1899 words). The variable
    %               word_indices contains the list of indices of the words
    %               which occur in one email.
    % 
    %               Concretely, if an email has the text:
    %
    %                  The quick brown fox jumped over the lazy dog.
    %
    %               Then, the word_indices vector for this text might look 
    %               like:
    %               
    %                   60  100   33   44   10     53  60  58   5
    %
    %               where, we have mapped each word onto a number, for example:
    %
    %                   the   -- 60
    %                   quick -- 100
    %                   ...
    %
    %              (note: the above numbers are just an example and are not the
    %               actual mappings).
    %
    %              Your task is take one such word_indices vector and construct
    %              a binary feature vector that indicates whether a particular
    %              word occurs in the email. That is, x(i) = 1 when word i
    %              is present in the email. Concretely, if the word 'the' (say,
    %              index 60) appears in the email, then x(60) = 1. The feature
    %              vector should look like:
    %             你的任务是取一个这样的word索引矢量和构造一个二元特征向量表示一个特定的
    %             电子邮件中出现了单词。也就是说，x（i）=1 在电子邮件中出现。具体来说，
    %             如果这个词是“the”（比如,索引60）出现在电子邮件中，然后x（60）=1。
    %              x = [ 0 0 0 0 1 0 0 0 ... 0 0 0 0 1 ... 0 0 0 1 0 ..];
    %
    %
     for i=1:length(word_indices)
         x(word_indices(i))=1;
       end;
    % =========================================================================
        
    end

%% Initialization
    clear ; close all; clc
    
    %% ==================== Part 1: Email Preprocessing ====================
    %  To use an SVM to classify emails into Spam v.s. Non-Spam, you first need
    %  to convert each email into a vector of features. In this part, you will
    %  implement the preprocessing steps for each email. You should
    %  complete the code in processEmail.m to produce a word indices vector
    %  for a given email.
    
    fprintf('\nPreprocessing sample email (emailSample1.txt)\n');
    
    % Extract Features
    file_contents = readFile('emailSample1.txt');
    word_indices  = processEmail(file_contents);
    
    % Print Stats
    fprintf('Word Indices: \n');
    fprintf(' %d', word_indices);
    fprintf('\n\n');
    
    fprintf('Program paused. Press enter to continue.\n');
    pause;
    
    %% ==================== Part 2: Feature Extraction ====================
    %  Now, you will convert each email into a vector of features in R^n. 
    %  You should complete the code in emailFeatures.m to produce a feature
    %  vector for a given email.
    
    fprintf('\nExtracting features from sample email (emailSample1.txt)\n');
    
    % Extract Features
    file_contents = readFile('emailSample1.txt');
    word_indices  = processEmail(file_contents);
    features      = emailFeatures(word_indices);
    
    % Print Stats
    fprintf('Length of feature vector: %d\n', length(features));
    fprintf('Number of non-zero entries: %d\n', sum(features > 0));
    
    fprintf('Program paused. Press enter to continue.\n');
    pause;
    
    %% =========== Part 3: Train Linear SVM for Spam Classification ========
    %  In this section, you will train a linear classifier to determine if an
    %  email is Spam or Not-Spam.
    
    % Load the Spam Email dataset
    % You will have X, y in your environment
    load('spamTrain.mat');
    
    fprintf('\nTraining Linear SVM (Spam Classification)\n')
    fprintf('(this may take 1 to 2 minutes) ...\n')
    
    C = 0.1;
    model = svmTrain(X, y, C, @linearKernel);
    
    p = svmPredict(model, X);
    
    fprintf('Training Accuracy: %f\n', mean(double(p == y)) * 100);
    
    %% =================== Part 4: Test Spam Classification ================
    %  After training the classifier, we can evaluate it on a test set. We have
    %  included a test set in spamTest.mat
    
    % Load the test dataset
    % You will have Xtest, ytest in your environment
    load('spamTest.mat');
    
    fprintf('\nEvaluating the trained Linear SVM on a test set ...\n')
    
    p = svmPredict(model, Xtest);
    
    fprintf('Test Accuracy: %f\n', mean(double(p == ytest)) * 100);
    pause;

%% ================= Part 5: Top Predictors of Spam ====================
    %  Since the model we are training is a linear SVM, we can inspect the
    %  weights learned by the model to understand better how it is determining
    %  whether an email is spam or not. The following code finds the words with
    %  the highest weights in the classifier. Informally, the classifier
    %  'thinks' that these words are the most likely indicators of spam.
    %
    
    % Sort the weights and obtin the vocabulary list
    [weight, idx] = sort(model.w, 'descend');
    vocabList = getVocabList();
    
    fprintf('\nTop predictors of spam: \n');
    for i = 1:15
        fprintf(' %-15s (%f) \n', vocabList{idx(i)}, weight(i));
    end
    
    fprintf('\n\n');
    fprintf('\nProgram paused. Press enter to continue.\n');
    pause;
    
    %% =================== Part 6: Try Your Own Emails =====================
    %  Now that you've trained the spam classifier, you can use it on your own
    %  emails! In the starter code, we have included spamSample1.txt,
    %  spamSample2.txt, emailSample1.txt and emailSample2.txt as examples. 
    %  The following code reads in one of these emails and then uses your 
    %  learned SVM classifier to determine whether the email is Spam or 
    %  Not Spam
    
    % Set the file to be read in (change this to spamSample2.txt,
    % emailSample1.txt or emailSample2.txt to see different predictions on
    % different emails types). Try your own emails as well!
    filename = 'spamSample1.txt';
    
    % Read and predict
    file_contents = readFile(filename);
    word_indices  = processEmail(file_contents);
    x             = emailFeatures(word_indices);
    p = svmPredict(model, x);
    
    fprintf('\nProcessed %s\n\nSpam Classification: %d\n', filename, p);
    fprintf('(1 indicates spam, 0 indicates not spam)\n\n');