Add .simplify argument in accumulate2()

Closes tidyverse#774

NEWS.md

@@ -11,6 +11,10 @@
   possible to disable the simplification by setting `.simplify` to
   `FALSE`.
 
+* `accumulate2()` gains a `.simplify` argument as well. It did not use
+  to simplify its output, but we've changed this default to
+  automatically simplify for consistency with `accumulate()`.
+
 * `accumulate()` now uses vctrs for simplifying the output. This
   ensures a more principled and flexible coercion behaviour.
 

R/reduce.R

@@ -476,8 +476,14 @@ accumulate <- function(.x,
 }
 #' @rdname accumulate
 #' @export
-accumulate2 <- function(.x, .y, .f, ..., .init) {
-  reduce2_impl(.x, .y, .f, ..., .init = .init, .acc = TRUE)
+accumulate2 <- function(.x, .y, .f, ..., .init, .simplify = TRUE) {
+  res <- reduce2_impl(.x, .y, .f, ..., .init = .init, .acc = TRUE)
+
+  if (.simplify) {
+    acc_simplify(res)
+  } else {
+    res
+  }
 }
 
 accumulate_names <- function(nms, init, dir) {

tests/testthat/test-reduce.R

@@ -172,8 +172,8 @@ test_that("basic accumulate2() works", {
   paste2 <- function(x, y, sep) paste(x, y, sep = sep)
 
   x <- c("a", "b", "c")
-  expect_equal(accumulate2(x, c("-", "."), paste2), list("a", "a-b", "a-b.c"))
-  expect_equal(accumulate2(x, c(".", "-", "."), paste2, .init = "x"), list("x", "x.a", "x.a-b", "x.a-b.c"))
+  expect_equal(accumulate2(x, c("-", "."), paste2), c("a", "a-b", "a-b.c"))
+  expect_equal(accumulate2(x, c(".", "-", "."), paste2, .init = "x"), c("x", "x.a", "x.a-b", "x.a-b.c"))
 })
 
 test_that("can terminate accumulate2() early", {
@@ -187,8 +187,8 @@ test_that("can terminate accumulate2() early", {
   }
 
   x <- c("a", "b", "c")
-  expect_equal(accumulate2(x, c("-", "."), paste2), list("a", "a-b"))
-  expect_equal(accumulate2(x, c(".", "-", "."), paste2, .init = "x"), list("x", "x.a", "x.a-b"))
+  expect_equal(accumulate2(x, c("-", "."), paste2), c("a", "a-b"))
+  expect_equal(accumulate2(x, c(".", "-", "."), paste2, .init = "x"), c("x", "x.a", "x.a-b"))
 })
 
 test_that("accumulate2() forces arguments (#643)", {