Introduction to Regular Expression

@(NLP)

[TOC]

導(dǎo)論

Q1 什么是Regular Expression？
Q2 Regular Expression 有什么用？
Q3 Regular Expression 怎么寫？
Q4 R中哪有寫實(shí)用的Regular Expression的包或者函數(shù)？

Definition

wiki: A regular expression, regex or regexp(sometimes called a rational expression) is, in theoretical computer science and formal language theory, a sequence of characters that define a search pattern. Usually this pattern is then used by string searching algorithms for "find" or "find and replace" operations on strings.

涉及的領(lǐng)域：theoretical computer science; formal language theory
內(nèi)涵：a sequence of characters that define a search pattern
通常運(yùn)用：used by string searching algorithms for "find" or "find and replace" operations on strings.

Basic concepts

A regular expression, often called a pattern, is an expression used to specify a set of strings required for a particular purpose.

features:

1. a simple way to specify
2. more concise ways to specify
3. the specification is not unique

operations to construct regular expressions:

1. Boolean（布爾數(shù)學(xué)體系的） "or"
   A vertical bar（豎線） separates alternatives. For example, gray|grey can match "gray" or "grey".

Boolean是否只能是兩者選？
alternatives表示可選擇的、備用的；沒(méi)有二選一的意思。

2. Grouping
   Parentheses（圓括號(hào)） are used to define the scope（范圍） and precedence（位次） of the operators (among other uses).For example, gray|grey and gr(a|e)y are equivalent patterns which both describe the set of "gray" or "grey".

參考

百度百科
wiki
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