Add functions: str_to_camel(), str_to_kebab(), str_to_snake() (#577)

Fixes #573

Author: librill

NAMESPACE

@@ -57,8 +57,11 @@ export(str_starts)
 export(str_sub)
 export(str_sub_all)
 export(str_subset)
+export(str_to_camel)
+export(str_to_kebab)
 export(str_to_lower)
 export(str_to_sentence)
+export(str_to_snake)
 export(str_to_title)
 export(str_to_upper)
 export(str_trim)

NEWS.md

@@ -1,5 +1,6 @@
 # stringr (development version)
 
+* New `str_to_camel()`, `str_to_snake()`, and `str_to_kebab()` for changing "programming" case (@librill, #573).
 * All relevant stringr functions now preserve names (@jonovik, #575).
 * New `vignette("locale-sensitive")` about locale sensitive functions (@kylieainslie, #404)
 * New `str_ilike()` that follows the conventions of the SQL ILIKE operator (@edward-burn, #543).

R/case.R

@@ -55,3 +55,68 @@ str_to_sentence <- function(string, locale = "en") {
   )
   copy_names(string, out)
 }
+
+
+#' Convert between different types of programming case
+#'
+#' @description
+#' * `str_to_camel()` converts to camel case, where the first letter of
+#'   each word is capitalized, with no separation between words. By default
+#'   the first letter of the first word is not capitalized.
+#'
+#' * `str_to_kebab()` converts to kebab case, where words are converted to
+#'   lower case and separated by dashes (`-`).
+#'
+#' * `str_to_snake()` converts to snake case, where words are converted to
+#'   lower case and separated by underscores (`_`).
+#' @inheritParams str_to_lower
+#' @export
+#' @param first_upper Logical. Should the first letter be capitalized?
+#' @examples
+#' str_to_camel("my-variable")
+#' str_to_camel("my-variable", first_upper = TRUE)
+#'
+#' str_to_snake("MyVariable")
+#' str_to_kebab("MyVariable")
+str_to_camel <- function(string, first_upper = FALSE) {
+  check_character(string)
+  check_bool(first_upper)
+
+  string <- string |>
+    to_words() |>
+    str_to_title() |>
+    str_remove_all(pattern = "\\s+")
+
+  if (!first_upper) {
+    str_sub(string, 1, 1) <- str_to_lower(str_sub(string, 1, 1))
+  }
+
+  string
+}
+#' @export
+#' @rdname str_to_camel
+str_to_snake <- function(string) {
+  check_character(string)
+  string |>
+    to_words() |>
+    str_replace_all(pattern = "\\s+", replacement = "_")
+}
+#' @export
+#' @rdname str_to_camel
+str_to_kebab <- function(string) {
+  check_character(string)
+  string |>
+    to_words() |>
+    str_replace_all(pattern = "\\s+", replacement = "-")
+}
+
+to_words <- function(string) {
+  string |>
+    str_replace_all("([a-z])([A-Z])", "\\1 \\2") |>
+    str_replace_all("([a-zA-Z])([0-9])", "\\1 \\2") |>
+    str_replace_all("([0-9])([a-zA-Z])", "\\1 \\2") |>
+    str_replace_all("([A-Z]+)([A-Z][a-z])", "\\1 \\2") |>
+    str_to_lower() |>
+    str_replace_all(pattern = "[:punct:]", replacement = " ") |>
+    str_trim()
+}

_pkgdown.yml

@@ -69,6 +69,7 @@ reference:
   - str_conv
   - str_like
   - str_replace_na
+  - str_to_camel
   - str_view
   - word
 

man/str_to_camel.Rd

@@ -10,7 +10,6 @@ test_that("to_title creates one capital letter per word", {
 })
 
 test_that("to_sentence capitalizes just the first letter", {
-  x <- "This is a sentence."
   expect_identical(str_to_sentence("a Test"), "A test")
 })
 
@@ -20,3 +19,30 @@ test_that("case conversions preserve names", {
   expect_equal(names(str_to_upper(x)), names(x))
   expect_equal(names(str_to_title(x)), names(x))
 })
+
+# programming cases -----------------------------------------------------------
+
+test_that("to_camel can control case of first argument", {
+  expect_equal(str_to_camel("my_variable"), "myVariable")
+  expect_equal(str_to_camel("my_variable", first_upper = TRUE), "MyVariable")
+})
+
+test_that("to_kebab converts to kebab case", {
+  expect_equal(str_to_kebab("myVariable"), "my-variable")
+  expect_equal(str_to_kebab("MyVariable"), "my-variable")
+  expect_equal(str_to_kebab("MyVariable1"), "my-variable-1")
+})
+
+test_that("to_snake converts to snake case", {
+  expect_equal(str_to_snake("myVariable"), "my_variable")
+  expect_equal(str_to_snake("MyVariable"), "my_variable")
+  expect_equal(str_to_snake("MyVariable1"), "my_variable_1")
+})
+
+test_that("to_words handles common compound cases", {
+  expect_equal(to_words("a_b"), "a b")
+  expect_equal(to_words("a-b"), "a b")
+  expect_equal(to_words("aB"), "a b")
+  expect_equal(to_words("a123b"), "a 123 b")
+  expect_equal(to_words("HTML"), "html")
+})