Implement special case where everything is nested.

Fixes tidyverse#186

NEWS.md

@@ -1,5 +1,7 @@
 # tidyr 0.4.1.9000
 
+* `nest()` now returns correct output if every variable is nested (#186).
+
 * `full_seq()` now preserve attributes for dates and date/times (#156).
 
 * Sequences generated by `full_seq()` no now longer need to start at 0.

R/nest.R

@@ -67,6 +67,14 @@ nest_.grouped_df <- function(data, key_col, nest_cols = character()) {
 
 nest_impl <- function(data, key_col, group_cols, nest_cols) {
   data <- dplyr::ungroup(data)
+
+  if (length(group_cols) == 0) {
+    df <- dplyr::data_frame(list(data))
+    names(df) <- key_col
+
+    return(df)
+  }
+
   nest_cols <- setdiff(nest_cols, group_cols)
 
   out <- dplyr::distinct_(dplyr::select_(data, .dots = group_cols))

tests/testthat/test-nest.R

@@ -36,3 +36,9 @@ test_that("puts data into the correct row", {
 
   expect_equal(out$data[[1]]$x, 1)
 })
+
+test_that("nesting everything yields a simple data frame", {
+  df <- dplyr::data_frame(x = 1:3, y = c("B", "A", "A"))
+  out <- nest(df, x, y)
+  expect_equal(out, dplyr::data_frame(data = list(df)))
+})