fix: Ensure single column dfs work with group_split()

Fixes #124

DESCRIPTION

@@ -19,7 +19,7 @@ Suggests:
     tinytest
 License: MIT + file LICENSE
 Encoding: UTF-8
-RoxygenNote: 7.2.1
+RoxygenNote: 7.2.3
 Roxygen: list(markdown = TRUE)
 VignetteBuilder: knitr
 Language: en-GB

R/group_split.R

@@ -10,8 +10,8 @@
 #' @details
 #' **Grouped `data.frame`s:**
 #'
-#' The primary use case for `group_split()` is with already groups `data.frame`s, typically a result of [group_by()]. In
-#' this case, `group_split()` only uses the first argument, the grouped `data.frame`, and warns when `...` is used.
+#' The primary use case for `group_split()` is with already grouped `data.frame`s, typically a result of [group_by()].
+#' In this case, `group_split()` only uses the first argument, the grouped `data.frame`, and warns when `...` is used.
 #'
 #' Because some of these groups may be empty, it is best paired with `group_keys()` which identifies the representatives
 #' of each grouping variable for the group.
@@ -60,7 +60,7 @@ group_split <- function(.data, ..., .keep = TRUE) {
   res <- split_into_groups(context$.data, groups)
   names(res) <- NULL
   if (!isTRUE(.keep)) {
-    res <- lapply(res, function(x) x[, !colnames(x) %in% groups])
+    res <- lapply(res, function(x) x[, !colnames(x) %in% groups, drop = FALSE])
   }
   any_empty <- unlist(lapply(res, function(x) !(nrow(x) == 0L)))
   res[any_empty]

R/nest_by.R

@@ -33,7 +33,18 @@ nest_by.grouped_df <- function(.data, ..., .key = "data", .keep = FALSE) {
   if (!missing(...)) {
     stop("Can't re-group while nesting. Either `ungroup()` first or don't supply arguments to `nest_by()`")
   }
-  res <- group_keys(.data)
-  res[[.key]] <- group_split(.data, ..., .keep = .keep)
-  do.call(group_by, list(res, as.symbol(group_vars(.data))))
+  nests <- group_split(.data, ..., .keep = TRUE)
+  groups <- group_vars(.data)
+  res <- lapply(
+    nests,
+    function(x) {
+      df <- x[1, groups, drop = FALSE]
+      df[[.key]] <- list(x[, !colnames(x) %in% groups, drop = FALSE])
+      df
+    }
+  )
+  res <- do.call(rbind, res)
+  rownames(res) <- NULL
+  res <- do.call(arrange, list(res, as.symbol(groups)))
+  do.call(group_by, list(res, as.symbol(groups)))
 }

inst/tinytest/test_nest_by.R

@@ -8,6 +8,26 @@ expect_equal(
   info = "nest_by() takes group names"
 )
 
+expect_equal(
+  mtcars |> select(mpg, cyl, am) |> nest_by(am, cyl),
+  {
+    res <- data.frame(
+      am = c(0, 0, 0, 1, 1, 1),
+      cyl = c(4, 6, 8, 4, 6, 8)
+    )
+    res[["data"]] <- list(
+      mtcars[mtcars$am == 0 & mtcars$cyl == 4, "mpg", drop = FALSE],
+      mtcars[mtcars$am == 0 & mtcars$cyl == 6, "mpg", drop = FALSE],
+      mtcars[mtcars$am == 0 & mtcars$cyl == 8, "mpg", drop = FALSE],
+      mtcars[mtcars$am == 1 & mtcars$cyl == 4, "mpg", drop = FALSE],
+      mtcars[mtcars$am == 1 & mtcars$cyl == 6, "mpg", drop = FALSE],
+      mtcars[mtcars$am == 1 & mtcars$cyl == 8, "mpg", drop = FALSE]
+    )
+    group_by(res, am)
+  },
+  info = "nest_by() works with only one non-group column (#124)"
+)
+
 expect_equal(
   mtcars %>% group_by(am) %>% nest_by(),
   {