From 9bda33c6d72a1d74d580ebba5391992a58f6afa5 Mon Sep 17 00:00:00 2001
From: Nat DeFries <42820733+nmdefries@users.noreply.github.com>
Date: Wed, 26 Apr 2023 12:41:13 -0400
Subject: [PATCH 1/3] pass ref_time_value to function f in epix_slide

---
 R/grouped_epi_archive.R |  6 +++---
 R/methods-epi_archive.R | 11 ++++++-----
 R/utils.R               |  5 +++--
 3 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/R/grouped_epi_archive.R b/R/grouped_epi_archive.R
index ac093e6f..ccac7c6d 100644
--- a/R/grouped_epi_archive.R
+++ b/R/grouped_epi_archive.R
@@ -222,7 +222,7 @@ grouped_epi_archive =
             
             # Check that `f` takes enough args
             if (!missing(f) && is.function(f)) {
-              check_sufficient_f_args(f)
+              check_sufficient_f_args(f, 3L)
             }
 
             # Validate and pre-process `before`:
@@ -278,7 +278,7 @@ grouped_epi_archive =
                                     comp_effective_key_vars,
                                     new_col) {
               # Carry out the specified computation
-              comp_value = f(.data_group, .group_key, ...)
+              comp_value = f(.data_group, .group_key, ref_time_value, ...)
 
               if (all_versions) {
                 # Extract data from archive so we can do length checks below. When
@@ -294,7 +294,7 @@ grouped_epi_archive =
               # Note: this mirrors how `epi_slide` does things if we're using
               # unique keys, but can diverge if using nonunique keys. The
               # `epi_slide` approach of counting occurrences of the
-              # `ref_time_value` in the `time_value` column, which helps lines
+              # `ref_time_value` in the `time_value` column, which helps line
               # up the computation results with corresponding rows of the
               # input data, wouldn't quite apply here: we'd want to line up
               # with rows (from the same group) with `version` matching the
diff --git a/R/methods-epi_archive.R b/R/methods-epi_archive.R
index 348c5c01..41ba585c 100644
--- a/R/methods-epi_archive.R
+++ b/R/methods-epi_archive.R
@@ -658,11 +658,12 @@ group_by.epi_archive = function(.data, ..., .add=FALSE, .drop=dplyr::group_by_dr
 #'   determined by the `before` parameter described below. One time step is
 #'   typically one day or one week; see [`epi_slide`] details for more
 #'   explanation. If a function, `f` must take `x`, an `epi_df` with the same
-#'   column names as the archive's `DT`, minus the `version` column; followed by
-#'   `g`, a one-row tibble containing the values of the grouping variables for
-#'   the associated group; followed by any number of named arguments. If a
-#'   formula, `f` can operate directly on columns accessed via `.x$var`, as in
-#'   `~ mean(.x$var)` to compute a mean of a column `var` for each
+#'   column names as the archive's `DT`, minus the `version` column; followed
+#'   by `g`, a one-row tibble containing the values of the grouping variables
+#'   for the associated group; followed by `t`, a Date containing the
+#'   reference time value to use; followed by any number of named arguments.
+#'   If a formula, `f` can operate directly on columns accessed via `.x$var`,
+#'   as in `~ mean(.x$var)` to compute a mean of a column `var` for each
 #'   `ref_time_value`-group combination. If `f` is missing, then `...` will
 #'   specify the computation.
 #' @param ... Additional arguments to pass to the function or formula specified
diff --git a/R/utils.R b/R/utils.R
index c953b385..7316b7dc 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -104,10 +104,11 @@ Warn = function(msg, ...) rlang::warn(break_str(msg, init = "Warning: "), ...)
 #'
 #' @param f Function; specifies a computation to slide over an `epi_df` or
 #'  `epi_archive` in `epi_slide` or `epix_slide`.
+#' @param n_mandatory_f_args Integer; specifies the number of arguments `f`
+#'  is required to take before any `...` arg. Defaults to 2.
 #'
 #' @noRd
-check_sufficient_f_args <- function(f) {
-  n_mandatory_f_args <- 2
+check_sufficient_f_args <- function(f, n_mandatory_f_args = 2L) {
   arg_names = names(formals(args(f)))
   if ("..." %in% arg_names) {
     # Keep all arg names before `...`

From c6329b1e62197a008d7f0a42db38ecfd952a3be2 Mon Sep 17 00:00:00 2001
From: Nat DeFries <42820733+nmdefries@users.noreply.github.com>
Date: Thu, 27 Apr 2023 15:40:34 -0400
Subject: [PATCH 2/3] bind ref_time_value to copy of execution env for f as
 formula or dots

---
 NAMESPACE               |  1 +
 R/grouped_epi_archive.R |  8 ++++++--
 man/epix_slide.Rd       | 11 ++++++-----
 3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/NAMESPACE b/NAMESPACE
index 10847e6c..a44561cf 100644
--- a/NAMESPACE
+++ b/NAMESPACE
@@ -89,6 +89,7 @@ importFrom(rlang,"!!")
 importFrom(rlang,.data)
 importFrom(rlang,.env)
 importFrom(rlang,arg_match)
+importFrom(rlang,child_env)
 importFrom(rlang,enquo)
 importFrom(rlang,enquos)
 importFrom(rlang,is_quosure)
diff --git a/R/grouped_epi_archive.R b/R/grouped_epi_archive.R
index ccac7c6d..aa456910 100644
--- a/R/grouped_epi_archive.R
+++ b/R/grouped_epi_archive.R
@@ -186,7 +186,7 @@ grouped_epi_archive =
 #'   object. See the documentation for the wrapper function [`epix_slide()`] for
 #'   details.
 #' @importFrom data.table key address
-#' @importFrom rlang !! !!! enquo quo_is_missing enquos is_quosure sym syms
+#' @importFrom rlang !! !!! enquo quo_is_missing enquos is_quosure sym syms child_env
           slide = function(f, ..., before, ref_time_values,
                            time_step, new_col_name = "slide_value",
                            as_list_col = FALSE, names_sep = "_",
@@ -364,7 +364,9 @@ grouped_epi_archive =
             # If f is not missing, then just go ahead, slide by group
             if (!missing(f)) {
               if (rlang::is_formula(f)) f = rlang::as_function(f)
+              f_init_env <- environment(f)
               x = purrr::map_dfr(ref_time_values, function(ref_time_value) {
+                environment(f) <- child_env(.parent = f_init_env, ref_time_value = ref_time_value)
                 # Ungrouped as-of data; `epi_df` if `all_versions` is `FALSE`,
                 # `epi_archive` if `all_versions` is `TRUE`:
                 as_of_raw = private$ungrouped$as_of(ref_time_value, min_time_value = ref_time_value - before, all_versions = all_versions)
@@ -437,10 +439,12 @@ grouped_epi_archive =
               }
               
               quo = quos[[1]]
-              f = function(x, quo, ...) rlang::eval_tidy(quo, x)
+              quo_init_env <- environment(quo)
               new_col = sym(names(rlang::quos_auto_name(quos)))
 
               x = purrr::map_dfr(ref_time_values, function(ref_time_value) {
+                environment(quo) <- child_env(.parent = quo_init_env, ref_time_value = ref_time_value)
+                f = function(x, quo, ...) rlang::eval_tidy(quo, x)
                 # Ungrouped as-of data; `epi_df` if `all_versions` is `FALSE`,
                 # `epi_archive` if `all_versions` is `TRUE`:
                 as_of_raw = private$ungrouped$as_of(ref_time_value, min_time_value = ref_time_value - before, all_versions = all_versions)
diff --git a/man/epix_slide.Rd b/man/epix_slide.Rd
index 54d16e86..f8d0e2da 100644
--- a/man/epix_slide.Rd
+++ b/man/epix_slide.Rd
@@ -28,11 +28,12 @@ sliding (a.k.a. "rolling") time window for each data group. The window is
 determined by the \code{before} parameter described below. One time step is
 typically one day or one week; see \code{\link{epi_slide}} details for more
 explanation. If a function, \code{f} must take \code{x}, an \code{epi_df} with the same
-column names as the archive's \code{DT}, minus the \code{version} column; followed by
-\code{g}, a one-row tibble containing the values of the grouping variables for
-the associated group; followed by any number of named arguments. If a
-formula, \code{f} can operate directly on columns accessed via \code{.x$var}, as in
-\code{~ mean(.x$var)} to compute a mean of a column \code{var} for each
+column names as the archive's \code{DT}, minus the \code{version} column; followed
+by \code{g}, a one-row tibble containing the values of the grouping variables
+for the associated group; followed by \code{t}, a Date containing the
+reference time value to use; followed by any number of named arguments.
+If a formula, \code{f} can operate directly on columns accessed via \code{.x$var},
+as in \code{~ mean(.x$var)} to compute a mean of a column \code{var} for each
 \code{ref_time_value}-group combination. If \code{f} is missing, then \code{...} will
 specify the computation.}
 

From 51bc3f09212044ea2b0039506d2608ce0c3de0e1 Mon Sep 17 00:00:00 2001
From: Nat DeFries <42820733+nmdefries@users.noreply.github.com>
Date: Thu, 27 Apr 2023 17:03:28 -0400
Subject: [PATCH 3/3] describe how to use ref_time_value in non-func
 computations

---
 R/methods-epi_archive.R | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/R/methods-epi_archive.R b/R/methods-epi_archive.R
index 41ba585c..53ba8801 100644
--- a/R/methods-epi_archive.R
+++ b/R/methods-epi_archive.R
@@ -665,7 +665,8 @@ group_by.epi_archive = function(.data, ..., .add=FALSE, .drop=dplyr::group_by_dr
 #'   If a formula, `f` can operate directly on columns accessed via `.x$var`,
 #'   as in `~ mean(.x$var)` to compute a mean of a column `var` for each
 #'   `ref_time_value`-group combination. If `f` is missing, then `...` will
-#'   specify the computation.
+#'   specify the computation. The reference time value can be accessed via
+#'   `ref_time_value` in a formula or in a computation defined in `...`.
 #' @param ... Additional arguments to pass to the function or formula specified
 #'   via `f`. Alternatively, if `f` is missing, then `...` is interpreted as an
 #'   expression for tidy evaluation. See details of [`epi_slide`].