在dplyr select中使用perl = TRUE正则表达式

快捷方式：

library(dplyr)

#notice the 3 colons because grep_vars is not exported from dplyr
matches2 <- function (match,ignore.case = TRUE,vars = current_vars()) 
{
  dplyr:::grep_vars(match,vars,ignore.case = ignore.case,perl = TRUE)
}

data.frame(baa=0,bAa=0) %>% select(matches2("(?i)b(?!a)"))
#boo boa
#1   0   0

或者更具解释性的解决方案

matches2 <- function (match,vars = current_vars()) 
{
  grep_vars2(match,ignore.case = ignore.case)
}

#this is pretty much my only change in the original dplyr:::grep_vars
#to make it accept perl.
grep_vars2 <- function (needle,...) 
{
  grep(needle,perl = TRUE,...)
}

 data.frame(baa=0,bAa=0) %>% 
   select(matches2("(?i)b(?!a)"))
 #boo boa
 #1   0   0