Is there a function to find all lower case letters in a character vector?

问题

I just wrote one, but I was wondering if one already exists in R.

Here's the function BTW (suggestions for improvement are welcome):

set.seed(50)
x <- sample(c(letters, LETTERS), 7)

is.lower <- function(x)
{
    unlist(sapply(x, function(x2) {x2 %in% letters}))
}

is.lower(x)

回答1:

grepl("[a-z]",x) for example?

> grepl("[a-z]",x)
[1] FALSE  TRUE  TRUE FALSE  TRUE  TRUE FALSE

And why make it difficult?

> x %in% letters
[1] FALSE  TRUE  TRUE FALSE  TRUE  TRUE FALSE

No need to make your own function.

回答2:

Another approach with the values instead of a logical index as the result, would be to name the letters as themselves and use "["with x as the index:

 names(letters) <- letters
 letters[x]
#<NA>    w    k <NA>    y    c <NA> 
#  NA  "w"  "k"   NA  "y"  "c"   NA 

来源：https://stackoverflow.com/questions/4423460/is-there-a-function-to-find-all-lower-case-letters-in-a-character-vector