July 2019
Intermediate to advanced
365 pages
8h 13m
Chinese
Content preview from Python机器学习手册：从数据预处理到深度学习
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23
第 2 章
加载数据
2.0
简介
只要涉及机器学习，第一个步骤都是把原始数据加载到系统中。原始数据可能是日志文
件、数据集文件或者数据库。此外，从多个源获取数据也很常见。本章讲解如何从不同
的源（包括
CSV
文件和
SQL
数据库）加载数据，同时也会介绍几种生成符合需求的仿
真实验数据的方法。尽管在
Python
生态体系中有很多加载数据的方法，但本书会着重使
用
pandas
库的一些方法来加载外部数据，并使用
scikit-learn
（
Python
中的一个开源的机
器学习库）来生成仿真数据。
2.1
加载样本数据集
问题描述
加载已有的样本数据集。
解决方案
scikit-learn
中预置了大量的流行数据集可供使用 ：
#
加载
scikit-learn
的数据集
from sklearn import datasets
#
加载手写数字数据集
digits = datasets.load_digits()
#
创建特征矩阵
24
｜
第
2
章
加载数据
features = digits.data
#
创建目标向量
target = digits.target
#
查看第一个样本数据
features[0]
array([ 0., 0., 5., 13., 9., 1., 0., 0., 0., 0., 13., ...
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