cat_dog <- function(x) { if (length(grep("(?=.*dog)", x, perl = TRUE) != 0)) {if (length(grep("(?=.*cat)", x, perl = TRUE)) != 0) {return(FALSE)} else {return(TRUE)}} else {return(FALSE)}}
cat_dog("asdfasdfasdf cat adsfafds dog")
cat_dog("asdfasdfasdf cat adsfafds")
cat_dog("asdfasdfasdf adsfafds dog")
cat_dog("asdfasdfasdf adsfafds")
cat_dog("asdfasdfasdf adsfafds dog abcd cat")