Add str_select which works as grep with value=T

R/select.r

@@ -0,0 +1,30 @@
+#' Keep only strings matching a pattern.
+#'
+#' Vectorised over \code{string} only.
+#'
+#' @param string input vector. This must be an atomic vector, and will be
+#'   coerced to a character vector
+#' @param pattern pattern to look for, as defined by a POSIX regular
+#'   expression.  See the ``Extended Regular Expressions'' section of 
+#'   \code{\link{regex}} for details.  See \code{\link{fixed}}, 
+#'   \code{\link{ignore.case}} and \code{\link{perl}} for how to use other
+#'   types of matching: fixed, case insensitive and perl-compatible.
+#' @return string vector
+#' @seealso \code{\link{grep}} with argument \code{value = TRUE}, 
+#'    \code{\link{str_detect}} for a version returning booleans for matches.
+#' @keywords character
+#' @export
+#' @examples
+#' fruit <- c("apple", "banana", "pear", "pinapple")
+#' str_select(fruit, "a")
+#' str_select(fruit, "^a")
+#' str_select(fruit, "a$")
+#' str_select(fruit, "b")
+#' str_select(fruit, "[aeiou]")
+#'
+str_select <- function(string, pattern) {
+  if (length(pattern) > 1) {
+    stop("Only one pattern can be used to select within a string")
+  }
+  string[which(str_detect(string, pattern))]
+}