Preserve list-cols in rowwise-across()

Fixes #6264

NEWS.md

@@ -1,5 +1,8 @@
 # dplyr (development version)
 
+* `across()` used without functions inside an rowwise-data frame no longer
+  generates an invalid data frame (#6264).
+
 * `arrange()` now correctly ignores `NULL` inputs (#6193).
 
 * `*_join()` now error if you supply them with additional arguments that

R/across.R

@@ -145,11 +145,11 @@ across <- function(.cols = everything(), .fns = NULL, ..., .names = NULL) {
   names <- setup$names
 
   mask <- peek_mask()
-  data <- mask$current_cols(vars)
 
   if (is.null(fns)) {
+    cols <- mask$current_cols(vars, restore_rowwise = TRUE)
     nrow <- length(mask$current_rows())
-    data <- new_data_frame(data, n = nrow, class = c("tbl_df", "tbl"))
+    data <- new_data_frame(cols, n = nrow, class = c("tbl_df", "tbl"))
 
     if (is.null(names)) {
       return(data)
@@ -158,6 +158,8 @@ across <- function(.cols = everything(), .fns = NULL, ..., .names = NULL) {
     }
   }
 
+  data <- mask$current_cols(vars)
+
   n_cols <- length(data)
   n_fns <- length(fns)
 

R/data-mask.R

@@ -72,21 +72,22 @@ DataMask <- R6Class("DataMask",
     },
 
     pick = function(vars) {
-      cols <- self$current_cols(vars)
-      if (inherits(private$data, "rowwise_df")) {
+      cols <- self$current_cols(vars, restore_rowwise = TRUE)
+      nrow <- length(self$current_rows())
+      new_tibble(cols, nrow = nrow)
+    },
+
+    current_cols = function(vars, restore_rowwise = FALSE) {
+      cols <- env_get_list(parent.env(private$mask), vars)
+      if (restore_rowwise && inherits(private$data, "rowwise_df")) {
         cols <- map2(cols, names(cols), function(col, name) {
           if (vec_is_list(private$current_data[[name]])) {
             col <- list(col)
           }
           col
         })
       }
-      nrow <- length(self$current_rows())
-      new_tibble(cols, nrow = nrow)
-    },
-
-    current_cols = function(vars) {
-      env_get_list(parent.env(private$mask), vars)
+      cols
     },
 
     current_rows = function() {

tests/testthat/test-across.R

@@ -897,6 +897,20 @@ test_that("expand_if_across() expands lambdas", {
   )
 })
 
+test_that("rowwise() preserves list-cols iff no fns (#5951, #6264)", {
+  rf <- rowwise(tibble(x = list(1:2, 3:5)))
+
+  # Need to unchop so works like mutate(x = length(x))
+  out <- mutate(rf, across(everything(), length))
+  expect_equal(out$x, c(2, 3))
+
+  # Need to preserve to create valid data frame
+  out <- mutate(rf, across = list(across(everything())))
+  expect_equal(out$across, list(
+    tibble(x = list(1:2)),
+    tibble(x = list(3:5))
+  ))
+})
 
 # c_across ----------------------------------------------------------------
 

tests/testthat/test-mutate.r

@@ -511,14 +511,6 @@ test_that("mutate() propagates caller env", {
   expect_caller_env(mutate(mtcars, sig_caller_env()))
 })
 
-test_that("rowwise() + mutate(across()) correctly handles list columns (#5951)", {
-  tib <- tibble(a=list(1:2,3:4),c=list(NULL,NULL)) %>% rowwise()
-  expect_identical(
-    mutate(tib, sum = across(everything(),sum)),
-    mutate(tib, sum = across(where(is.list),sum))
-  )
-})
-
 test_that("mutate() fails on named empty arguments (#5925)", {
   expect_error(
     mutate(tibble(), bogus = )