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Given the following text description, write Python code to implement the functionality described below step by step
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Description:
 EX 4
Step1:  (二)準備測試資料
利用make_classification產生分類資料，n_features=2表示共有兩個特徵, n_informative=2 代表有兩個類別
所產生之 X
Step2:  (三)測試分類器並作圖
接下來這段程式碼有兩個for 迴圈，外迴圈走過三個的dataset，內迴圈則走過所有的分類器。
為求簡要說明，我們將程式碼簡略如下：
1. 外迴圈：資料迴圈。首先畫出資料分佈，接著將資料傳入分類器迴圈
    python
    for ds in datasets
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Python Code:
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.colors import ListedColormap
from sklearn.cross_validation import train_test_split
from sklearn.preprocessing import StandardScaler
from sklearn.datasets import make_moons, make_circles, make_classification
from sklearn.neighbors import KNeighborsClassifier
from sklearn.svm import SVC
from sklearn.tree import DecisionTreeClassifier
from sklearn.ensemble import RandomForestClassifier, AdaBoostClassifier
from sklearn.naive_bayes import GaussianNB
from sklearn.discriminant_analysis import LinearDiscriminantAnalysis
from sklearn.discriminant_analysis import QuadraticDiscriminantAnalysis
h = .02  # step size in the mesh
names = ["Nearest Neighbors", "Linear SVM", "RBF SVM", "Decision Tree",
         "Random Forest", "AdaBoost", "Naive Bayes", "Linear Discriminant Ana.",
         "Quadratic Discriminant Ana."]
classifiers = [
    KNeighborsClassifier(3),
    SVC(kernel="linear", C=0.025),
    SVC(gamma=2, C=1),
    DecisionTreeClassifier(max_depth=5),
    RandomForestClassifier(max_depth=5, n_estimators=10, max_features=1),
    AdaBoostClassifier(),
    GaussianNB(),
    LinearDiscriminantAnalysis(),
    QuadraticDiscriminantAnalysis()]
Explanation: EX 4: Classifier comparison
這個範例的主要目的
* 比較各種分類器
* 利用圖示法觀察各種分類器的分類邊界及區域
(一)引入函式並準備分類器
將分類器引入之後存放入一個list裏
這邊要注意 sklearn.discriminant_analysis 必需要 sklearn 0.17以上才能執行
End of explanation
X, y = make_classification(n_features=2, n_redundant=0, n_informative=2,
                           random_state=1, n_clusters_per_class=1)
rng = np.random.RandomState(2)
X += 2 * rng.uniform(size=X.shape)
linearly_separable = (X, y)
datasets = [make_moons(noise=0.3, random_state=0),
            make_circles(noise=0.2, factor=0.5, random_state=1),
            linearly_separable
            ]
Explanation: (二)準備測試資料
利用make_classification產生分類資料，n_features=2表示共有兩個特徵, n_informative=2 代表有兩個類別
所產生之 X: 100 x 2矩陣，y: 100 元素之向量，y的數值僅有0或是1用來代表兩種類別
利用X += 2 * rng.uniform(size=X.shape)加入適度的雜訊後將(X,y)資料集命名為linear_separable
最後利用make_moon()及make_circles()產生空間中月亮形狀及圓形之數據分佈後，一併存入datasets變數
End of explanation
%matplotlib inline
figure = plt.figure(figsize=(30,20), dpi=300)
i = 1
# iterate over datasets
for ds in datasets:
    # preprocess dataset, split into training and test part
    X, y = ds
    X = StandardScaler().fit_transform(X)
    X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=.4)
    x_min, x_max = X[:, 0].min() - .5, X[:, 0].max() + .5
    y_min, y_max = X[:, 1].min() - .5, X[:, 1].max() + .5
    xx, yy = np.meshgrid(np.arange(x_min, x_max, h),
                         np.arange(y_min, y_max, h))
    # just plot the dataset first
    cm = plt.cm.RdBu
    cm_bright = ListedColormap(['#FF0000', '#0000FF'])
    ax = plt.subplot(len(datasets), (len(classifiers) + 1)//2, i)
    # Plot the training points
    ax.scatter(X_train[:, 0], X_train[:, 1], c=y_train, cmap=cm_bright)
    # and testing points
    ax.scatter(X_test[:, 0], X_test[:, 1], c=y_test, cmap=cm_bright, alpha=0.6)
    ax.set_xlim(xx.min(), xx.max())
    ax.set_ylim(yy.min(), yy.max())
    ax.set_xticks(())
    ax.set_yticks(())
    i += 1
    # iterate over classifiers
    for name, clf in zip(names[0:4], classifiers[0:4]):
        ax = plt.subplot(len(datasets), (len(classifiers) + 1)//2, i)
        clf.fit(X_train, y_train)
        score = clf.score(X_test, y_test)
        # Plot the decision boundary. For that, we will assign a color to each
        # point in the mesh [x_min, m_max]x[y_min, y_max].
        if hasattr(clf, "decision_function"):
            Z = clf.decision_function(np.c_[xx.ravel(), yy.ravel()])
        else:
            Z = clf.predict_proba(np.c_[xx.ravel(), yy.ravel()])[:, 1]
        # Put the result into a color plot
        Z = Z.reshape(xx.shape)
        ax.contourf(xx, yy, Z, cmap=cm, alpha=.8)
        # Plot also the training points
        ax.scatter(X_train[:, 0], X_train[:, 1], c=y_train, cmap=cm_bright)
        # and testing points
        ax.scatter(X_test[:, 0], X_test[:, 1], c=y_test, cmap=cm_bright,
                   alpha=0.6)
        ax.set_xlim(xx.min(), xx.max())
        ax.set_ylim(yy.min(), yy.max())
        ax.set_xticks(())
        ax.set_yticks(())
        ax.set_title(name,fontsize=28)
        ax.text(xx.max() - .3, yy.min() + .3, ('%.2f' % score).lstrip('0'),
                size=30, horizontalalignment='right')
        i += 1
figure.subplots_adjust(left=.02, right=.98)
plt.show()
Explanation: (三)測試分類器並作圖
接下來這段程式碼有兩個for 迴圈，外迴圈走過三個的dataset，內迴圈則走過所有的分類器。
為求簡要說明，我們將程式碼簡略如下：
1. 外迴圈：資料迴圈。首先畫出資料分佈，接著將資料傳入分類器迴圈
    python
    for ds in datasets:
        X, y = ds
        #調整特徵值大小使其在特定範圍
        X = StandardScaler().fit_transform(X)
        #利用train_test_split將資料分成訓練集以及測試集
        X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=.4)
        #產生資料網格來大範圍測試分類器，範例EX 3有詳述該用法
        xx, yy = np.meshgrid(..........省略)
        # 畫出訓練資料點
        ax.scatter(X_train[:, 0], X_train[:, 1], c=y_train, cmap=cm_bright)
        # 畫出測試資料點，用alpha=0.6將測試資料點畫的"淡"一些
        ax.scatter(X_test[:, 0], X_test[:, 1], c=y_test, cmap=cm_bright, alpha=0.6)
2. 內迴圈：分類器迴圈。測試分類準確度並繪製分類邊界及區域
    ```python
    for name, clf in zip(names, classifiers):
        clf.fit(X_train, y_train)
        score = clf.score(X_test, y_test)
    # Plot the decision boundary. For that, we will assign a color to each
    # point in the mesh [x_min, m_max]x[y_min, y_max].
    if hasattr(clf, "decision_function"):
        Z = clf.decision_function(np.c_[xx.ravel(), yy.ravel()])
    else:
        Z = clf.predict_proba(np.c_[xx.ravel(), yy.ravel()])[:, 1]
    # Put the result into a color plot
    Z = Z.reshape(xx.shape)
    ax.contourf(xx, yy, Z, cmap=cm, alpha=.8)
```
為了顯示方便，我將原始碼的內圈改為 for name, clf in zip(names[0:4], classifiers[0:4]):只跑過前四個分類器。
End of explanation
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