在R中使用正则表达式从链接中提取字符串

问题描述

我有一个URL链接列表，我想提取一个字符串并将它们保存在另一个变量中。示例数据如下：

  sample<-  c("http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr01f2009.pdf","http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr02f2001.pdf","http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr03f2002.pdf","http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr04f2004.pdf","http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr05f2005.pdf","http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr06f2018.pdf","http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr07f2016.pdf","http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr08f2015.pdf","http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr09f2020.pdf","http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr10f2014.pdf")

sample

 [1] "http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr01f2009.pdf"
 [2] "http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr02f2001.pdf"
 [3] "http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr03f2002.pdf"
 [4] "http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr04f2004.pdf"
 [5] "http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr05f2005.pdf"
 [6] "http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr06f2018.pdf"
 [7] "http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr07f2016.pdf"
 [8] "http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr08f2015.pdf"
 [9] "http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr09f2020.pdf"
[10] "http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr10f2014.pdf"

我想使用正则表达式提取星期和年份。

     week year
1     1 2009
2     2 2001
3     3 2002
4     4 2004
5     5 2005
6     6 2018
7     7 2016
8     8 2015
9     9 2020
10   10 2014

解决方法

您可以使用str_match来捕获'owgr'和'f'之后的数字：

library(stringr)
str_match(sample,'owgr(\\d+)f(\\d+)')[,-1]

您可以将其转换为数据框，将类更改为数字并分配列名称。

setNames(type.convert(data.frame(
          str_match(sample,-1])),c('year','week'))

#   year week
#1     1 2009
#2     2 2001
#3     3 2002
#4     4 2004
#5     5 2005
#6     6 2018
#7     7 2016
#8     8 2015
#9     9 2020
#10   10 2014

---

另一种方法可能是从sample的最后一部分提取所有数字。我们可以使用basename来获取最后一部分。

str_extract_all(basename(sample),'\\d+',simplify = TRUE)

,

另一种尝试的方式

library(dplyr)
library(stringr)
df <- data.frame(sample)
df2 <- df %>% 
  transmute(year = str_extract(sample,"(?<=wgr)\\d{1,2}(?=f)"),week = str_extract(sample,"(?<=f)\\d{4}(?=\\.pdf)"))

#     year week
# 1     1 2009
# 2     2 2001
# 3     3 2002
# 4     4 2004
# 5     5 2005
# 6     6 2018
# 7     7 2016
# 8     8 2015
# 9     9 2020
# 10   10 2014

,

您可以使用 {unglue} ：

library(unglue)

unglue_data(
  sample,"http://dps.endavadigital.net/owgr/doc/content/archive/2009/owgr{week}f{year}.pdf")
#>    week year
#> 1    01 2009
#> 2    02 2001
#> 3    03 2002
#> 4    04 2004
#> 5    05 2005
#> 6    06 2018
#> 7    07 2016
#> 8    08 2015
#> 9    09 2020
#> 10   10 2014