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).

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)

R/epi_df_forbidden_methods.R

@@ -0,0 +1,38 @@
+# 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` can'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$colname)). You may
+                     also prefer to use the specialized `epi_slide_mean` method."))
+}
+
+# Similarly, provide better error messages for some other potentially-common
+# slide operations (sum, prod, min, max, all, any, range):
+
+#' @export
+Summary.epi_df <- function(..., na.rm = FALSE) {
+  generic <- .Generic # cli uses dot prefixes for special purpose, don't upset it
+  maybe_opt_pointer <- switch(
+    .Generic,
+    sum = "You may also prefer the specialized epi_slide_sum method.",
+    prod =, min =, max =, all =, any = "You may also prefer the specialized epi_slide_opt method.",
+    range = "",
+    cli_abort("Unrecognized .Generic: {generic}")
+  )
+  cli_abort(c("`{generic}` can't be used on entire `epi_df`s",
+              "x" = "{rlang::caller_arg(..1)} was an `epi_df`",
+              "i" = "If you encountered this while trying to take a rolling {generic}
+                     of a column using `epi_slide`, you probably forgot to
+                     specify the column name (e.g., ~ mean(.x$colname)).
+                     {maybe_opt_pointer}"))
+}