当模式不太清楚时，在R中提取子字符串

Question

I started R a week ago and I've been working on extracting some information from htmls to get started.

I know this is a frequent and basic question, because I've already asked it in a different context and I read quite a few threads.

I also know the functions I could use: sub / str_match, etc.

I chose to use sub() and here is what my code looks like for the time being:

#libraries
library('xml2')
library('rvest')
library('stringr')

#author page:
url <- paste('https://ideas.repec.org/e/',sample[4,3],'.html',sep="")
url <- gsub(" ", "", url, fixed = TRUE)
webpage <- read_html(url)

#get all published articles:
list_articles <- html_text(html_nodes(webpage,'#articles-body ol > li'))

#get titles:
titles <- html_text(html_nodes(webpage, '#articles-body b a'))

#get co-authors:
authors <- sub(".* ([A-Za-z_]+),([0-9]+).\n.*","\\1", list_articles)

Here is what an element of list_articles looks like:

" Theo Sparreboom & Lubna Shahnaz, 2007.\n\"Assessing Labour Market 
Vulnerability among Young People,\"\nThe Pakistan Development 
Review,\nPakistan Institute of Development Economics, vol. 46(3), pages 193-
213.\n"  

When I try to get the co-authors, R gives me the whole string instead of just the co-authors, so I'm clearly specifying the pattern incorrectly, but I don't get why.

If someone could help me out, that would be great.

Hope you have a good day, G. Gauthier

Answer 1

Is this helpful?

It says extract the string from the first upper case letter until there is a comma, space and then digit.

library(stringr)

#get co-authors:
authors <- str_extract(list_articles,"[[:upper:]].*(?=, [[:digit:]])")