Apply vctrs principles to map() and modify() (#894)

New `map_vec()`, `map2_vec()`, and `pmap_vec()` return a vector the same length as `x` with type determined by the returned type of `.f`. Fixes #435

`modify()`, `modify_if()`, `modify_at()`, and `modify2()` have been rewritten from scratch. They are no longer generic and should work with a wider range of (future) classes from the vctrs package. Fixes #928

All the tests for these functions have been substantially revamped to do a better job of illustrating the underlying invariants.

NAMESPACE

@@ -4,27 +4,6 @@ S3method(as_mapper,character)
 S3method(as_mapper,default)
 S3method(as_mapper,list)
 S3method(as_mapper,numeric)
-S3method(modify,character)
-S3method(modify,default)
-S3method(modify,double)
-S3method(modify,integer)
-S3method(modify,logical)
-S3method(modify,pairlist)
-S3method(modify2,character)
-S3method(modify2,default)
-S3method(modify2,double)
-S3method(modify2,integer)
-S3method(modify2,logical)
-S3method(modify_at,character)
-S3method(modify_at,default)
-S3method(modify_at,double)
-S3method(modify_at,integer)
-S3method(modify_at,logical)
-S3method(modify_if,character)
-S3method(modify_if,default)
-S3method(modify_if,double)
-S3method(modify_if,integer)
-S3method(modify_if,logical)
 S3method(print,purrr_function_compose)
 S3method(print,purrr_function_partial)
 S3method(print,purrr_rate_backoff)
@@ -152,6 +131,7 @@ export(map2_dfr)
 export(map2_int)
 export(map2_lgl)
 export(map2_raw)
+export(map2_vec)
 export(map_at)
 export(map_chr)
 export(map_dbl)
@@ -163,6 +143,7 @@ export(map_if)
 export(map_int)
 export(map_lgl)
 export(map_raw)
+export(map_vec)
 export(modify)
 export(modify2)
 export(modify_at)
@@ -184,6 +165,7 @@ export(pmap_dfr)
 export(pmap_int)
 export(pmap_lgl)
 export(pmap_raw)
+export(pmap_vec)
 export(possibly)
 export(prepend)
 export(pwalk)

NEWS.md

@@ -70,6 +70,10 @@
 * `*_at()` can now take a function (or formula) that's passed the vector of
   element names and returns the elements to select.
 
+* New `map_vec()`, `map2_vec()`, and `pmap_vec()` work on all types of vectors,
+  extending `map_lgl()`, `map_int()`, and friends so that you can easily work
+  with dates, factors, date-times and more (#435).
+
 * New `keep_at()` and `discard_at()` that work like `keep()` and `discard()`
   but operation on element names rather than element contents (#817).
 
@@ -78,6 +82,11 @@
 
 * purrr is now licensed as MIT (#805).
 
+* `modify()`, `modify_if()`, `modify_at()`, and `modify2()` are no longer
+  generics. We have discovered a simple implementation that no longer requires
+  genericity and methods were only provided by a very small number of packages
+  (#894).
+
 * purrr now uses the base pipe (`|>`) and anonymous function short hand (`\(x)`),
   in all examples. This means that examples will no longer work in R 4.0 and 
   earlier so in those versions of R, the examples are automatically converted 
@@ -122,6 +131,10 @@
 * `map2()` and `pmap()` now recycle names of their first input if
   needed (#783).
 
+* `modify()`, `modify_if()`, and `modify_at()` have been reimplemented using
+  vctrs principles. This shouldn't have an user facing impact, but it does
+  make the implementation much simpler.
+
 ### Plucking
 
 * `vec_depth()` is now `pluck_depth()` and works with more types of input
@@ -160,6 +173,8 @@
 
 ## Minor improvements and bug fixes
 
+* `modify()` no longer supports modifying calls or pairlists.
+
 * `modify_depth()` is no longer a generic. This makes it more consistent
   with `map_depth()`.
 

R/map.R

@@ -12,6 +12,9 @@
 #'   atomic vector of the indicated type (or die trying). For these functions,
 #'   `.f` must return a length-1 vector of the appropriate type.
 #'
+#' * `map_vec()` simplifies to the common type of the output. It works with
+#'   most types of simple vectors like Date, POSIXct, factors, etc.
+#'
 #' * `walk()` calls `.f` for its side-effect and returns
 #'   the input `.x`.
 #'
@@ -36,15 +39,20 @@
 #'   for details.
 #' @returns
 #' The output length is determined by the length of the input.
+#' The output names are determined by the input names.
 #' The output type is determined by the suffix:
 #'
-#' * No suffix: a list.
+#' * No suffix: a list; `.f()` can return anything.
+#'
+#' * `_lgl()`, `_int()`, `_dbl()`, `_chr()` return a logical, integer, double,
+#'   or character vector respectively; `.f()` must return a compatible atomic
+#'   vector of length 1.
 #'
-#' * `_lgl`, `_int`, `_dbl`, `_chr` return a logical, integer, double,
-#'   or character vector respectively. It will be named if the input was named.
+#' * `_vec()` return an atomic or S3 vector, the same type that `.f` returns.
+#'   `.f` can return pretty much any type of vector, as long as its length 1.
 #'
 #' * `walk()` returns the input `.x` (invisibly). This makes it easy to
-#'    use in a pipe.
+#'    use in a pipe. The return value of `.f()` is ignored.
 #' @export
 #' @family map variants
 #' @seealso [map_if()] for applying a function to only those elements
@@ -116,23 +124,33 @@ map_lgl <- function(.x, .f, ..., .progress = FALSE) {
 
 #' @rdname map
 #' @export
-map_chr <- function(.x, .f, ..., .progress = FALSE) {
+map_int <- function(.x, .f, ..., .progress = FALSE) {
   .f <- as_mapper(.f, ...)
-  .Call(map_impl, environment(), ".x", ".f", "character", .progress)
+  .Call(map_impl, environment(), ".x", ".f", "integer", .progress)
 }
 
 #' @rdname map
 #' @export
-map_int <- function(.x, .f, ..., .progress = FALSE) {
+map_dbl <- function(.x, .f, ..., .progress = FALSE) {
   .f <- as_mapper(.f, ...)
-  .Call(map_impl, environment(), ".x", ".f", "integer", .progress)
+  .Call(map_impl, environment(), ".x", ".f", "double", .progress)
 }
 
 #' @rdname map
 #' @export
-map_dbl <- function(.x, .f, ..., .progress = FALSE) {
+map_chr <- function(.x, .f, ..., .progress = FALSE) {
   .f <- as_mapper(.f, ...)
-  .Call(map_impl, environment(), ".x", ".f", "double", .progress)
+  .Call(map_impl, environment(), ".x", ".f", "character", .progress)
+}
+
+#' @rdname map
+#' @param .ptype If `NULL`, the default, the output type is the common type
+#'   of the elements of the result. Otherwise, supply a "prototype" giving
+#'   the desired type of output.
+#' @export
+map_vec <- function(.x, .f, ..., .ptype = NULL, .progress = FALSE) {
+  out <- map(.x, .f, ..., .progress = .progress)
+  simplify_impl(out, ptype = .ptype)
 }
 
 #' @rdname map

R/map2.R

@@ -64,11 +64,16 @@ map2_chr <- function(.x, .y, .f, ..., .progress = NULL) {
   .Call(map2_impl, environment(), ".x", ".y", ".f", "character", .progress)
 }
 
+#' @rdname map2
+#' @export
+map2_vec <- function(.x, .y, .f, ..., .ptype = NULL, .progress = NULL) {
+  out <- map2(.x, .y, .f, ..., .progress = .progress)
+  simplify_impl(out, ptype = .ptype)
+}
 
 #' @export
 #' @rdname map2
 walk2 <- function(.x, .y, .f, ...) {
   map2(.x, .y, .f, ...)
   invisible(.x)
 }
-