1.从一串字符中提取数字

#extract digits - all 4 works
string <- "My roll number is 1006781"
gsub(pattern = "[^0-9]",replacement = "",x = string)
stringi::stri_extract_all_regex(str = string,pattern = "\\d+") #list
regmatches(string, regexpr("[0-9]+",string))
regmatches(string, regexpr("[[:digit:]]+",string))

2.从一串字符串中删除空格

#remove space
gsub(pattern = "[[:space:]]",replacement = "",x = "and going there today tomorrow")
gsub(pattern = "[[:blank:]]",replacement = "",x = "and going there today tomorrow")
gsub(pattern = "\\s",replacement = "",x = "and going there today tomorrow")

3.如果向量中存在值，则返回

#match values
det <- c("A1","A2","A3","A4","A5","A6","A7")
grep(pattern = "A1|A4",x = det,value =T)

4.提取键值对中可用的字符串

d <- c("(monday :: 0.1231313213)","tomorrow","(tuesday :: 0.1434343412)")
grep(pattern = "\\([az]+ :: (0\\.[0-9]+)\\)",x = d,value = T)
regmatches(d,regexpr(pattern = "\\((.*) :: (0\\.[0-9]+)\\)",text = d))

说明：您可能会发现理解起来很复杂，所以让我们一点一点地看一下。 “\（”用于转义元字符。“[az] +”匹配字母一次或多次。“（0 \。[0-9] +）”匹配十进制值，其中元字符（。）被转义使用双反斜杠，周期也是如此。使用“[0-9] +”匹配数字。