机器学习实战（8）—— 支持向量机代码实现
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邮政系统每天都会收到大量的信件，最为要紧的一环是要根据信件上的收信人邮编进行识别和分类，以便确定信件的投送地。
原本这项任务是依靠大量的人工来进行，后来人们尝试让计算机来代替人工。然而，因为多数的邮编都是手写的数字，并且样式各异，所以没有统一编制的规则可以用于很好的识别和分类。
机器学习兴起之后，大量研究表明svm可以在手写体数字图片的分类任务上展现出很好的性能。
首先，导入手写字体：
# 从sklearn.datasets里导入手写体数字加载器。
from sklearn.datasets import load_digits
# 从通过数据加载器获得手写体数字的数码图像数据并储存在digits变量中。
digits = load_digits()
可以看一下数据：
digits
数据如下，是2维向量形式，表示手写数字：
{'DESCR': "Optical Recognition of Handwritten Digits Data Set\n===================================================\n\nNotes\n-----\nData Set Characteristics:\n :Number of Instances: 5620\n :Number of Attributes: 64\n :Attribute Information: 8x8 image of integer pixels in the range 0..16.\n :Missing Attribute Values: None\n :Creator: E. Alpaydin (alpaydin '@' boun.edu.tr)\n :Date: July; 1998\n\nThis is a copy of the test set of the UCI ML hand-written digits datasets\nhttp://archive.ics.uci.edu/ml/datasets/Optical+Recognition+of+Handwritten+Digits\n\nThe data set contains images of hand-written digits: 10 classes where\neach class refers to a digit.\n\nPreprocessing programs made available by NIST were used to extract\nnormalized bitmaps of handwritten digits from a preprinted form. From a\ntotal of 43 people, 30 contributed to the training set and different 13\nto the test set. 32x32 bitmaps are divided into nonoverlapping blocks of\n4x4 and the number of on pixels are counted in each block. This generates\nan input matrix of 8x8 where each element is an integer in the range\n0..16. This reduces dimensionality and gives invariance to small\ndistortions.\n\nFor info on NIST preprocessing routines, see M. D. Garris, J. L. Blue, G.\nT. Candela, D. L. Dimmick, J. Geist, P. J. Grother, S. A. Janet, and C.\nL. Wilson, NIST Form-Based Handprint Recognition System, NISTIR 5469,\n1994.\n\nReferences\n----------\n - C. Kaynak (1995) Methods of Combining Multiple Classifiers and Their\n Applications to Handwritten Digit Recognition, MSc Thesis, Institute of\n Graduate Studies in Science and Engineering, Bogazici University.\n - E. Alpaydin, C. Kaynak (1998) Cascading Classifiers, Kybernetika.\n - Ken Tang and Ponnuthurai N. Suganthan and Xi Yao and A. Kai Qin.\n Linear dimensionalityreduction using relevance weighted LDA. School of\n Electrical and Electronic Engineering Nanyang Technological University.\n 2005.\n - Claudio Gentile. A New Approximate Maximal Margin Classification\n Algorithm. NIPS. 2000.\n",
'data': array([[ 0., 0., 5., ..., 0., 0., 0.],
[ 0., 0., 0., ..., 10., 0., 0.],
[ 0., 0., 0., ..., 16., 9., 0.],
...,
[ 0., 0., 1., ..., 6., 0., 0.],
[ 0., 0., 2., ..., 12., 0., 0.],
[ 0., 0., 10., ..., 12., 1., 0.]]),
'images': array([[[ 0., 0., 5., ..., 1., 0., 0.],
[ 0., 0., 13., ..., 15., 5., 0.],
[ 0., 3., 15., ..., 11., 8., 0.],
...,
[ 0., 4., 11., ..., 12., 7., 0.],
[ 0., 2., 14., ..., 12., 0., 0.],
[ 0., 0., 6., ..., 0., 0., 0.]],
[[ 0., 0., 0., ..., 5., 0., 0.],
[ 0., 0., 0., ..., 9., 0., 0.],
[ 0., 0., 3., ..., 6., 0., 0.],
...,
[ 0., 0., 1., ..., 6., 0., 0.],
[ 0., 0., 1., ..., 6., 0., 0.],
[ 0., 0., 0., ..., 10., 0., 0.]],
[[ 0., 0., 0., ..., 12., 0., 0.],
[ 0., 0., 3., ..., 14., 0., 0.],
[ 0., 0., 8., ..., 16., 0., 0.],
...,
[ 0., 9., 16., ..., 0., 0., 0.],
[ 0., 3., 13., ..., 11., 5., 0.],
[ 0., 0., 0., ..., 16., 9., 0.]],
...,
[[ 0., 0., 1., ..., 1., 0., 0.],
[ 0., 0., 13., ..., 2., 1., 0.],
[ 0., 0., 16., ..., 16., 5., 0.],
...,
[ 0., 0., 16., ..., 15., 0., 0.],
[ 0., 0., 15., ..., 16., 0., 0.],
[ 0., 0., 2., ..., 6., 0., 0.]],
[[ 0., 0., 2., ..., 0., 0., 0.],
[ 0., 0., 14., ..., 15., 1., 0.],
[ 0., 4., 16., ..., 16., 7., 0.],
...,
[ 0., 0., 0., ..., 16., 2., 0.],
[ 0., 0., 4., ..., 16., 2., 0.],
[ 0., 0., 5., ..., 12., 0., 0.]],
[[ 0., 0., 10., ..., 1., 0., 0.],
[ 0., 2., 16., ..., 1., 0., 0.],
[ 0., 0., 15., ..., 15., 0., 0.],
...,
[ 0., 4., 16., ..., 16., 6., 0.],
[ 0., 8., 16., ..., 16., 8., 0.],
[ 0., 1., 8., ..., 12., 1., 0.]]]),
'target': array([0, 1, 2, ..., 8, 9, 8]),
'target_names': array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9])}
# 检视数据规模和特征维度。
digits.data.shape
手写数字的图像数据共有1797条，每幅图片是8*8=64的像素矩阵表示,在模型使用这些像素矩阵时，我们习惯将2D的图片像素矩阵逐行收尾拼接为1D的像素特征向量。
接下来切分训练集和测试集：
# 从sklearn.cross_validation中导入train_test_split用于数据分割。
from sklearn.cross_validation import train_test_split
# 随机选取75%的数据作为训练样本；其余25%的数据作为测试样本。
X_train, X_test, y_train, y_test = train_test_split(digits.data, digits.target, test_size=0.25, random_state=33)
y_train.shape
y_test.shape
接下来导入数据标准化模块，并且导入SVM模型
# 从sklearn.preprocessing里导入数据标准化模块。
from sklearn.preprocessing import StandardScaler
# 从sklearn.svm里导入基于线性假设的支持向量机分类器LinearSVC。
from sklearn.svm import LinearSVC
对数据进行标准化
# 从仍然需要对训练和测试的特征数据进行标准化。
ss = StandardScaler()
X_train = ss.fit_transform(X_train)
X_test = ss.transform(X_test)
使用SVM进行训练和预测：
# 初始化线性假设的支持向量机分类器LinearSVC。
lsvc = LinearSVC()
#进行模型训练
lsvc.fit(X_train, y_train)
# 利用训练好的模型对测试样本的数字类别进行预测，预测结果储存在变量y_predict中。
y_predict = lsvc.predict(X_test)
输出预测精度：
# 使用模型自带的评估函数进行准确性测评。
print('The Accuracy of Linear SVC is', lsvc.score(X_test, y_test))
输出更详细的评估报告：
# 依然使用sklearn.metrics里面的classification_report模块对预测结果做更加详细的分析。
from sklearn.metrics import classification_report
print(classification_report(y_test, y_predict, target_names=digits.target_names.astype(str)))#转为字符
以上就是Python实现SVM对手写字体识别分类，你学会了么？