如何使用stringr将列串括号内最后出现的字符串提取到另一列中？

Question

我在列中有一组随机文本，就像这样。

dplyr::tibble(text = c("I have a (brown) clock", "surrounded by (red) walls", "inside of a (blue) building with (dirty) windows",
                      "where (magical) things (unexpectedly) occur (spontaneously)"))

# A tibble: 4 x 1
  text                                                       
  <chr>                                                      
1 I have a (brown) clock                                     
2 surrounded by (red) walls                                  
3 inside of a (blue) building with (dirty) windows           
4 where (magical) things (unexpectedly) occur (spontaneously)

我想把括号内最后出现的字符串 提取到另一列中 这样看起来就像这样了

dplyr::tibble(text = c("I have a (brown) clock", "surrounded by (red) walls", "inside of a (blue) building with (dirty) windows",
                          "where (magical) things (unexpectedly) occur (spontaneously)"),
                  extract = c("brown", "red", "dirty", "spontaneously"))

# A tibble: 4 x 2
  text                                                        extract      
  <chr>                                                       <chr>        
1 I have a (brown) clock                                      brown        
2 surrounded by (red) walls                                   red          
3 inside of a (blue) building with (dirty) windows            dirty        
4 where (magical) things (unexpectedly) occur (spontaneously) spontaneously

Answer 1

一个选项是 stri_extract_last 从 stringi 而且应该很快。 在这里，我们做一个regex lookaround来匹配开头的括号((?<=\\())后跟一个或多个非括号的字符([^\\)]+)

library(dplyr)
df1 %>%
    mutate(extract = stringi::stri_extract_last(text, regex = "(?<=\\()[^\\)]+"))
# A tibble: 4 x 2
#  text                                                        extract      
#  <chr>                                                       <chr>        
#1 I have a (brown) clock                                      brown        
#2 surrounded by (red) walls                                   red          
#3 inside of a (blue) building with (dirty) windows            dirty        
#4 where (magical) things (unexpectedly) occur (spontaneously) spontaneously