regex - 使用正则表达式从字符串中提取

Question

我有一个字符串：

s <- "test.test AS field1, ablh.blah AS field2, faslk.lsdf AS field3"

我想转换为：

"field1, field2, field3"

我知道正则表达式(\w+)(?:,|$)会提取我想要的字符串（'field1'等），但我不知道如何用gsub.

Answer 1

## Preparation
s <- "test.test AS field1, ablh.blah AS field2, faslk.lsdf AS field3"
pat <- "(\\w+)(?:,|$)"  ## Note the doubly-escaped \\w

## Use the powerful gregexpr/regmatches one-two punch
m <- gregexpr(pat, s)
paste(regmatches(s, m)[[1]], collapse=" ")
# [1] "field1, field2, field3"

Answer 2

在gsubfn 包strapplyc中，可以使用一个特别简单的正则表达式来完成它，该表达式提取后面的每个单词字符串（如果该字段可以包含非单词字符，则用适当的表达式替换，例如任何不是空格的字符或逗号：）：" AS "\\w[^ ,]

> library(gsubfn)
> strapplyc(s, " AS (\\w+)", simplify = toString)[[1]]
[1] "field1, field2, field3"