August 2018
Intermediate to advanced
227 pages
4h 16m
Chinese
Content preview from 高效R语言编程
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166
｜
第
8
章
3.
确认你安装了
64
位
R
。
4.
云计算是成本低廉的获取更强计算能力的方法。
5.
固态硬盘通常对你的
R
代码的速度影响不大，但提升了你整体工作效率，
因为它的
I/O
很快。
背景知识：什么是字节？
一个计算机不能直接存储“数字”或“字母”。计算机只能存储和处理“位”。
“位”是二进制，只能是
0
或者
1
。事实上，从物理的角度看，一个二进制位（比
特）只是代表电的变化：有或无。
过去，计算机主要使用
ASCII
字符集，它定义了
128
个字符，包括
0
到
9
、
大小写字母、小量类似换行符之类的控制字符。
保存这些字符需要
7
比特，
因为
2
7
= 128
，但因性能原因常用
8
比特。表
8-1
列出了一些字符的二进制表示。
表
8
-
1
：一些字符的 ASCII 码
二进制形式
字符
01000001 A
01000010 B
01000011 C
01000100 D
01000101 E
01010010 R
因为
ASCII
码只有
256
个字符的限制，所以引入了
Unicode
，
Unicode
是为每
个合理的书写系统创建单一字符集的标准框架。通常，
Unicode
字符需要用
16
位保存。
8
位（比特）是一个字节，能存一个
ASCII
码字符。所以两个
ASCII
码字符
将使用两个字节或者
16
位。包含
100
个字符的纯文本文档需要使用
100
字节
（
800
比特）。注意类似字体或者元数据，会额外增加相当大的内存开销：一
个空的
.docx
文件大约需要
3700
字节的存储空间。
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