R 根据一些观察结果提取文本中的第一个括号

我有一些数据看起来像：

# A tibble: 5 x 3
  grp   LP                                                      RE                                           
  <chr> <chr>                                                   <chr>                                        
1 4999  " PLATTEVILLE, Colo., Dec. 30, 2011 /PRNewswire/ -- Sy… " usa : United States | usco : Colorado | us…
2 9122  " 14:22 ET - Facebook (FB) has hired Campbell Brown, a… " usa : United States | namz : North America…
3 161   " DALLAS (Dow Jones)--Pioneer National Resources Co. (… " usa : United States | ustx : Texas | namz …

我们可以使用str_匹配：

这将捕获圆括号中的所有内容，并在其前面加上可选的“-”

我们可以使用str\u匹配：

---

这将捕获圆括号中的所有内容，并在其前面加上可选的“-”

如果行中有“-”，则查找“-”之后的第一个括号，否则查找第一个括号

lapply(dat$LP, 
       function(x){
           # split the text where there is --
           x_0 <- (x %>% strsplit('--'))[[1]]
           # if the text contains the string '--' 
           # then length(x_0) is more than 1
           if(length(x_0) > 1){
               # remove the first part of the split, paste the rest back together
               # meaning: start looking for the brackets after '--'
               x <- paste(x_0[-1], collapse = ' ')
           } # else we'll look for the brackets in the full string
           # find where there's brackets in the text
           pos <- gregexpr("\\(.*?\\)", x)[[1]]
           # get the position of the first occurence
           start <- pos[1]
           # get the length of the first occurence
           leng <- attr(pos, "match.length")[1]
           # extract the string
           res <- substr(x, start, start+leng)
           return(res)
       })

---

如果行中有“-”，那么在“-”之后查找第一个括号，否则查找第一个括号

lapply(dat$LP, 
       function(x){
           # split the text where there is --
           x_0 <- (x %>% strsplit('--'))[[1]]
           # if the text contains the string '--' 
           # then length(x_0) is more than 1
           if(length(x_0) > 1){
               # remove the first part of the split, paste the rest back together
               # meaning: start looking for the brackets after '--'
               x <- paste(x_0[-1], collapse = ' ')
           } # else we'll look for the brackets in the full string
           # find where there's brackets in the text
           pos <- gregexpr("\\(.*?\\)", x)[[1]]
           # get the position of the first occurence
           start <- pos[1]
           # get the length of the first occurence
           leng <- attr(pos, "match.length")[1]
           # extract the string
           res <- substr(x, start, start+leng)
           return(res)
       })

我们可以先使用stri_extract_和str_remove

我们可以先使用stri_extract_和str_remove

lapply(dat$LP, 
       function(x){
           # split the text where there is --
           x_0 <- (x %>% strsplit('--'))[[1]]
           # if the text contains the string '--' 
           # then length(x_0) is more than 1
           if(length(x_0) > 1){
               # remove the first part of the split, paste the rest back together
               # meaning: start looking for the brackets after '--'
               x <- paste(x_0[-1], collapse = ' ')
           } # else we'll look for the brackets in the full string
           # find where there's brackets in the text
           pos <- gregexpr("\\(.*?\\)", x)[[1]]
           # get the position of the first occurence
           start <- pos[1]
           # get the length of the first occurence
           leng <- attr(pos, "match.length")[1]
           # extract the string
           res <- substr(x, start, start+leng)
           return(res)
       })

library(stringr)
library(stringi)
str_remove(stri_extract_first(df1$LP, regex = "--?[^(]+\\([^\\)]+\\)"), 
                "^[^\\(]+")
#[1] "(NYSE Amex: SYRG)" "(FB)"              "(PXD)"             NA                  NA