R 仅提取正则表达式中模式的第二个实例

我试图使用编程语言

R

、版本4.0.2和

stringr

包中的正则表达式从字符串中提取模式的第二个实例

> test_string <- "Viscocity                      S   <=0.25        S   <=0.25 Levorotatory                      S      <=21        R      <=2.5 Giminal                    S      <=1        S      <=1"

---

>test_string您可以将下面的模式与
str_match
一起使用：

(?<=Levorotatory)(?:\s*([SRI]|N/I)\s*([^\w\s]*\d*\.?\d+)){2}

"S      <=21"

regex <- "(\\s*(?:S|R|I|N/I)(\\s*\\W*\\d*\\.?\\d?\\d?\\d?\\s*)){2}"
str_trim(str_extract_all(test_string, glue('(?<=Levorotatory){regex}')))
output: "S      <=21        R      <=2.5"

(?<=Levorotatory)(?:\s*([SRI]|N/I)\s*([^\w\s]*\d*\.?\d+)){2}

library(stringr)
pattern <- "(?<=Levorotatory)(?:\\s*([SRI]|N/I)\\s*([^\\w\\s]*\\d*\\.?\\d+)){2}";
x <- "Viscocity                      S   <=0.25        S   <=0.25 Levorotatory                      S      <=21        R      <=2.5 Giminal                    S      <=1        S      <=1"
results <- str_match(x, pattern)[,-1]
results
# => [1] "R"     "<=2.5"