Remove unnecessary/misleading select.epi_df implementation

`select.epi_df` looked weird:
- `reclass(selected, attr(selected, "metadata"))` would only have made sense if
  grouped_df had a `select` that dropped our class but not our metadata,
  implemented in a way that called our own impls for `dplyr_extending` that would
  make that metadata actually be correct (in the case of renaming).
- (`dplyr_reconstruct(selected, selected)` might have made sense, if `reclass`
  acted on something that shouldn't actually become an `epi_df`, decaying back to
  a non-`epi_df` only if needed.)

So it seemed like it relied on `dplyr_extending` being almost, but not quite,
sufficient. But it looks like `grouped_df` doesn't even have a `select` impl, so
it's not interfering anyway! So it looks like we can just get rid of our own
impl.

Author: brookslogan

NAMESPACE

@@ -38,7 +38,6 @@ S3method(next_after,integer)
 S3method(print,epi_archive)
 S3method(print,epi_df)
 S3method(print,grouped_epi_archive)
-S3method(select,epi_df)
 S3method(summary,epi_df)
 S3method(ungroup,epi_df)
 S3method(ungroup,grouped_epi_archive)

R/group_by_epi_df_methods.R

@@ -3,11 +3,3 @@
 # `epi_df`s. It would be nice if there were a way to replace these with a
 # generic core that automatically fixed all misbehaving methods; see
 # brainstorming within Issue #223.
-
-#' @importFrom dplyr select
-#' @export
-select.epi_df <- function(.data, ...) {
-  selected <- NextMethod(.data)
-  might_decay <- reclass(selected, attr(selected, "metadata"))
-  return(dplyr_reconstruct(might_decay, might_decay))
-}

tests/testthat/test-methods-epi_df.R

@@ -173,11 +173,30 @@ test_that("Renaming columns while grouped gives appropriate colnames and metadat
   expect_identical(attr(renamed_gedf1, "metadata")$other_keys, c("age_group"))
   # renaming using select
   renamed_gedf2 <- gedf %>%
-    as_epi_df(additional_metadata = list(other_keys = "age")) %>%
     select(geo_value, time_value, age_group = age, value)
   expect_identical(renamed_gedf1, renamed_gedf2)
 })
 
+test_that("Additional `select` on `epi_df` tests", {
+  edf <- tibble::tibble(geo_value = "ak", time_value = as.Date("2020-01-01"), age = 1, value = 1) %>%
+    as_epi_df(additional_metadata = list(other_keys = "age"))
+
+  # Dropping a non-geo_value epikey column doesn't decay, though maybe it
+  # should, since you'd expect that to possibly result in multiple rows per
+  # epikey (though not in this toy case), and while we don't require that, we
+  # sort of expect it:
+  edf_not_decayed <- edf %>%
+    select(geo_value, time_value, value)
+  expect_class(edf_not_decayed, "epi_df")
+  expect_identical(attr(edf_not_decayed, "metadata")$other_keys, character(0L))
+
+  # Dropping geo_value does decay:
+  edf_decayed <- edf %>%
+    select(age, time_value, value)
+  expect_false(inherits(edf_decayed, "epi_df"))
+  expect_identical(attr(edf_decayed, "metadata"), NULL)
+})
+
 test_that("complete.epi_df works", {
   start_date <- as.Date("2020-01-01")
   daily_edf <- tibble::tribble(