feat(epi_slide): catch common operations x forgotten colname

See #475. We have the ability to catch this consistently now since we are using
`.keep = TRUE`, so the .x into each slide computation is an `epi_df` even if
we're grouping by `geo_value` (previously, .x would have decayed into a tibble
and we shouldn't override tibble's behavior).

Also add missing `group_map` import.

Author: brookslogan

DESCRIPTION

@@ -79,6 +79,7 @@ Collate:
     'correlation.R'
     'data.R'
     'epi_df.R'
+    'epi_df_forbidden_methods.R'
     'epiprocess.R'
     'group_by_epi_df_methods.R'
     'methods-epi_archive.R'

NAMESPACE

@@ -2,6 +2,7 @@
 
 S3method("[",epi_df)
 S3method("names<-",epi_df)
+S3method(Summary,epi_df)
 S3method(arrange_canonical,default)
 S3method(arrange_canonical,epi_df)
 S3method(as_epi_df,data.frame)
@@ -36,6 +37,7 @@ S3method(key_colnames,data.frame)
 S3method(key_colnames,default)
 S3method(key_colnames,epi_archive)
 S3method(key_colnames,epi_df)
+S3method(mean,epi_df)
 S3method(next_after,Date)
 S3method(next_after,integer)
 S3method(print,epi_archive)
@@ -148,6 +150,7 @@ importFrom(dplyr,everything)
 importFrom(dplyr,filter)
 importFrom(dplyr,group_by)
 importFrom(dplyr,group_by_drop_default)
+importFrom(dplyr,group_map)
 importFrom(dplyr,group_modify)
 importFrom(dplyr,group_vars)
 importFrom(dplyr,groups)

R/epi_df_forbidden_methods.R

@@ -0,0 +1,48 @@
+# Methods in this file are used to
+# * Disable problematic inherited behavior (e.g., mean on epi_dfs)
+# * Provide better error messaging if possible for things that already abort
+#   when they should (e.g., sum on epi_dfs)
+
+
+# Disable mean on epi_dfs, to prevent `epi_slide(~ mean(.x), ....)` bad output:
+
+#' @export
+mean.epi_df <- function(x, ...) {
+  cli_abort(c(
+    "`mean` shouldn't be used on entire `epi_df`s",
+    "x" = "{rlang::caller_arg(x)} was an `epi_df`",
+    "i" = "If you encountered this while trying to take a rolling mean
+           of a column using `epi_slide`, you probably forgot to
+           specify the column name (e.g., ~ mean(.x$colname)). You may
+           also prefer to use the specialized `epi_slide_mean` method."
+  ))
+}
+
+# Similarly, provide better error messages for some other potentially-common
+# slide operations (sum, prod, min, max, all, any, range):
+
+#' @export
+Summary.epi_df <- function(..., na.rm = FALSE) {
+  # cli uses dot prefixes for special purpose; use alias to avoid confusion during interpolation
+  generic <- .Generic
+  opt_pointer <- switch(.Generic,
+    sum = "You may also prefer to use the specialized `epi_slide_sum` method.",
+    prod = ,
+    min = ,
+    max = ,
+    all = ,
+    any = "You may also prefer to use the specialized `epi_slide_opt` method.",
+    range = "",
+    cli_abort("Unrecognized .Generic: {generic}")
+  )
+  cli_abort(c(
+    "`{generic}` shouldn't be used on entire `epi_df`s",
+    # We'd like to quote user input in the error message, but `caller_arg(..1)` is
+    # just "..1" and (eagerness/S4/unnamedness?) issues thwart some alternatives; just
+    # use something generic:
+    "x" = "`{generic}`'s first argument was an `epi_df`",
+    "i" = "If you encountered this while trying to take a rolling {generic}
+           of a column using `epi_slide`, you probably forgot to
+           specify the column name (e.g., ~ mean(.x$colname)). {opt_pointer}"
+  ))
+}

R/slide.R

@@ -36,7 +36,7 @@
 #' @template basic-slide-details
 #'
 #' @importFrom lubridate days weeks
-#' @importFrom dplyr bind_rows group_vars filter select
+#' @importFrom dplyr bind_rows group_map group_vars filter select
 #' @importFrom rlang .data .env !! enquos sym env missing_arg
 #' @export
 #' @seealso [`epi_slide_opt`] [`epi_slide_mean`] [`epi_slide_sum`]