Use tidyverse recycling rules

NEWS.md

@@ -38,6 +38,10 @@
 
 ## Features and fixes
 
+* `map2()`, `modify2()`, and `pmap()` now use tidyverse recycling rules where
+  vectors of length 1 are recycled to any size but all others must have
+  the same length (#878).
+
 * `list_modify()`'s interface has been standardised. Modifying with `NULL`
   now always creates a `NULL` in the output and we no longer recurse into
   data frames (and other objects built on top of lists that are fundamentally

R/modify.R

@@ -336,18 +336,9 @@ modify2 <- function(.x, .y, .f, ...) {
 }
 #' @export
 modify2.default <- function(.x, .y, .f, ...) {
-  .f <- as_mapper(.f, ...)
-
-  args <- recycle_args(list(.x, .y))
-  .x <- args[[1]]
-  .y <- args[[2]]
-
-  for (i in seq_along(.x)) {
-    list_slice2(.x, i) <- .f(.x[[i]], .y[[i]], ...)
-  }
-
-  .x
+  modify_base(map2, .x, .y, .f, ...)
 }
+
 #' @rdname modify
 #' @export
 imodify <- function(.x, .f, ...) {
@@ -373,11 +364,14 @@ modify2.logical  <- function(.x, .y, .f, ...) {
 }
 
 modify_base <- function(mapper, .x, .y, .f, ...) {
-  args <- recycle_args(list(.x, .y))
-  .x <- args[[1]]
-  .y <- args[[2]]
+  .f <- as_mapper(.f, ...)
+  out <- mapper(.x, .y, .f, ...)
 
-  .x[] <- mapper(.x, .y, .f, ...)
+  # if .x got recycled by map2
+  if (length(out) > length(.x)) {
+    .x <- .x[rep(1L, length(out))]
+  }
+  .x[] <- out
   .x
 }
 

R/pmap.R

@@ -10,6 +10,9 @@
 #'   arguments that `.f` will be called with. Arguments will be supply by
 #'   position if unnamed, and by name if named.
 #'
+#'   Vectors of length 1 will be recycled to any length; all other elements
+#'   must be have the same length.
+#'
 #'   A data frame is an important special case of `.l`. It will cause `.f`
 #'   to be called once for each row.
 #' @param .f A function, specified in one of the following ways:

R/utils.R

@@ -18,16 +18,6 @@ at_selection <- function(nm, .at){
   .at
 }
 
-recycle_args <- function(args) {
-  lengths <- map_int(args, length)
-  n <- max(lengths)
-
-  stopifnot(all(lengths == 1L | lengths == n))
-  to_recycle <- lengths == 1L
-  args[to_recycle] <- lapply(args[to_recycle], function(x) rep.int(x, n))
-  args
-}
-
 #' Infix attribute accessor
 #'
 #' @description

src/map.c

@@ -111,21 +111,15 @@ SEXP map2_impl(SEXP env, SEXP x_name_, SEXP y_name_, SEXP f_name_, SEXP type_) {
   check_vector(y_val, ".y");
 
   int nx = Rf_length(x_val), ny = Rf_length(y_val);
-  if (nx == 0 || ny == 0) {
-    SEXP out = PROTECT(Rf_allocVector(type, 0));
-    copy_names(x_val, out);
-    UNPROTECT(3);
-    return out;
-  }
-  if (nx != ny && !(nx == 1 || ny == 1)) {
+  if (nx != ny && nx != 1 && ny != 1) {
     Rf_errorcall(R_NilValue,
                  "Mapped vectors must have consistent lengths:\n"
                  "* `.x` has length %d\n"
                  "* `.y` has length %d",
                  nx,
                  ny);
   }
-  int n = (nx > ny) ? nx : ny;
+  int n = (nx == 1) ? ny : nx;
 
   // Constructs a call like f(x[[i]], y[[i]], ...)
   SEXP one = PROTECT(Rf_ScalarInteger(1));
@@ -150,9 +144,10 @@ SEXP pmap_impl(SEXP env, SEXP l_name_, SEXP f_name_, SEXP type_) {
     stop_bad_type(l_val, "a list", NULL, l_name);
   }
 
-  // Check all elements are lists and find maximum length
+  // Check all elements are lists and find recycled length
   int m = Rf_length(l_val);
-  int n = 0;
+  int has_scalar = 0;
+  int n = -1;
   for (int j = 0; j < m; ++j) {
     SEXP j_val = VECTOR_ELT(l_val, j);
 
@@ -161,28 +156,20 @@ SEXP pmap_impl(SEXP env, SEXP l_name_, SEXP f_name_, SEXP type_) {
     }
 
     int nj = Rf_length(j_val);
-
-    if (nj == 0) {
-      SEXP out = PROTECT(Rf_allocVector(type, 0));
-      copy_names(j_val, out);
-      UNPROTECT(2);
-      return out;
+    if (nj == 1) {
+      has_scalar = 1;
+      continue;
     }
 
-    if (nj > n) {
+    if (n == -1) {
       n = nj;
+    } else if (nj != n) {
+      stop_bad_element_length(j_val, j + 1, n, NULL, ".l", true);
     }
-
   }
 
-  // Check length of all elements
-  for (int j = 0; j < m; ++j) {
-    SEXP j_val = VECTOR_ELT(l_val, j);
-    int nj = Rf_length(j_val);
-
-    if (nj != 1 && nj != n) {
-      stop_bad_element_length(j_val, j + 1, n, NULL, ".l", true);
-    }
+  if (n == -1) {
+    n = has_scalar ? 1 : 0;
   }
 
   SEXP l_names = PROTECT(Rf_getAttrib(l_val, R_NamesSymbol));

tests/testthat/_snaps/map2.md

@@ -0,0 +1,10 @@
+# map2 recycles inputs
+
+    Code
+      map2(1:2, 1:3, `+`)
+    Condition
+      Error:
+      ! Mapped vectors must have consistent lengths:
+      * `.x` has length 2
+      * `.y` has length 3
+

tests/testthat/_snaps/pmap.md

@@ -0,0 +1,16 @@
+# inputs are recycled
+
+    Code
+      pmap(list(1:2, 1:3), identity)
+    Condition
+      Error in `stop_bad_length()`:
+      ! Element 2 of `.l` must have length 1 or 2, not 3
+
+---
+
+    Code
+      pmap(list(1:2, integer()), identity)
+    Condition
+      Error in `stop_bad_length()`:
+      ! Element 2 of `.l` must have length 1 or 2, not 0
+

tests/testthat/test-map2.R

@@ -1,14 +1,3 @@
-test_that("map2 inputs must be same length", {
-  expect_error(
-    map2(1:3, 2:3, function(...) NULL),
-    paste_line(
-      "Mapped vectors must have consistent lengths:",
-      "\\* `.x` has length 3",
-      "\\* `.y` has length 2"
-    )
-  )
-})
-
 test_that("map2 can't simplify if elements longer than length 1", {
   expect_bad_element_vector_error(
     map2_int(1:4, 5:8, range),
@@ -21,19 +10,14 @@ test_that("fails on non-vectors", {
   expect_bad_type_error(map2("a", environment(), identity), "`.y` must be a vector, not an environment")
 })
 
-test_that("map2 vectorised inputs of length 1", {
-  expect_equal(map2(1:2, 1, `+`), list(2, 3))
-  expect_equal(map2(1, 1:2, `+`), list(2, 3))
-})
+test_that("map2 recycles inputs", {
+  expect_equal(map2(1, 1, `+`), list(2))
 
-test_that("any 0 length input gives 0 length output", {
-  expect_equal(map2(list(), list(), ~ 1), list())
-  expect_equal(map2(1:10, list(), ~ 1), list())
-  expect_equal(map2(list(), 1:10, ~ 1), list())
+  expect_equal(map2(1:2, 1, `+`), list(2, 3))
+  expect_equal(map2(integer(), 1, `+`), list())
+  expect_equal(map2(NULL, 1, `+`), list())
 
-  expect_equal(map2(NULL, NULL, ~ 1), list())
-  expect_equal(map2(1:10, NULL, ~ 1), list())
-  expect_equal(map2(NULL, 1:10, ~ 1), list())
+  expect_snapshot(map2(1:2, 1:3, `+`), error = TRUE)
 })
 
 test_that("map2 takes only names from x", {
@@ -57,13 +41,9 @@ test_that("map2() with empty input copies names", {
   expect_identical(map2_chr(named_list, list(), identity), named(chr()))
 })
 
-test_that("map2() and pmap() recycle names (#779)", {
+test_that("map2() recycle names (#779)", {
   expect_identical(
     map2(c(a = 1), 1:2, ~ .x),
     list(a = 1, a = 1)
   )
-  expect_identical(
-    pmap(list(c(a = 1), 1:2), ~ .x),
-    list(a = 1, a = 1)
-  )
 })

tests/testthat/test-pmap.R

@@ -3,21 +3,15 @@ test_that("input must be a list of vectors", {
   expect_bad_type_error(pmap(list(environment()), identity), "Element 1 of `.l` must be a vector, not an environment")
 })
 
-test_that("elements must be same length", {
-  expect_bad_element_length_error(pmap(list(1:2, 1:3), identity), "Element 1 of `.l` must have length 1 or 3, not 2")
-})
-
-test_that("handles any length 0 input", {
-  expect_equal(pmap(list(list(), list(), list()), ~ 1), list())
-  expect_equal(pmap(list(NULL, NULL, NULL), ~ 1), list())
+test_that("inputs are recycled", {
+  expect_equal(pmap(list(1, 1), c), list(c(1, 1)))
+  expect_equal(pmap(list(1:2, 1), c), list(c(1, 1), c(2, 1)))
 
-  expect_equal(pmap(list(list(), list(), 1:10), ~ 1), list())
-  expect_equal(pmap(list(NULL, NULL, 1:10), ~ 1), list())
-})
+  expect_equal(pmap(list(list(), 1), ~ 1), list())
+  expect_equal(pmap(list(NULL, 1), ~ 1), list())
 
-test_that("length 1 elemetns are recycled", {
-  out <- pmap(list(1:2, 1), c)
-  expect_equal(out, list(c(1, 1), c(2, 1)))
+  expect_snapshot(pmap(list(1:2, 1:3), identity), error = TRUE)
+  expect_snapshot(pmap(list(1:2, integer()), identity), error = TRUE)
 })
 
 test_that(".f called with named arguments", {
@@ -30,6 +24,13 @@ test_that("names are preserved", {
   expect_equal(names(out), c("x", "y"))
 })
 
+test_that("pmap() recycles names (#779)", {
+  expect_identical(
+    pmap(list(c(a = 1), 1:2), ~ .x),
+    list(a = 1, a = 1)
+  )
+})
+
 test_that("... are passed on", {
   out <- pmap(list(x = 1:2), list, n = 1)
   expect_equal(out, list(
@@ -66,7 +67,7 @@ test_that("pmap on data frames performs rowwise operations", {
 })
 
 test_that("pmap works with empty lists", {
-  expect_identical(pmap(list(), identity), list())
+  expect_identical(pmap(list(), ~ 1), list())
 })
 
 test_that("preserves S3 class of input vectors (#358)", {