R中的正则表达式负向后看

不确定如何在R中实现它, .*(?<!See) (item 7 .*) 工作 sub ,只需注意see后面的空格和可以忽略的字母大小写 ignore.case 参数

sub(".*(?<!See) (item 7 .*)", "\\1", s, ignore.case = T, perl = T)

# [1] "Item 7 Management's Discussion and Analysis. BlahBlahBlah. Item 8 Financial Statements and Supplementary Data."

另一种选择:

sub(".*(?=(?<!See) ?item 7)", "", s, ignore.case = T, perl = T)
# [1] "Item 7 Management's Discussion and Analysis. BlahBlahBlah. Item 8 Financial Statements and Supplementary Data."

具有 str_extract_all() 从…起 stringr 包,它似乎没有提供 忽略.case 选项,您可以使用 [Ii] 要忽略此情况:

library(stringr)
str_extract_all(s, "(?<!See )[Ii]tem 7(.*)")
# [1] "Item 7 Management's Discussion and Analysis. BlahBlahBlah. Item 8 Financial Statements and Supplementary Data."