Allow process for grouped packers

R/packer-grouped.R

@@ -49,6 +49,16 @@
 ##' @param shared Names of the elements in `scalar` and `array` that
 ##'   are shared among all groups.
 ##'
+##' @param process An arbitrary R function that will be passed the
+##'   final assembled list **for each region**; it may create any
+##'   *additional* entries, which will be concatenated onto the
+##'   original list.  If you use this you should take care not to
+##'   return any values with the same names as entries listed in
+##'   `scalar`, `array` or `fixed`, as this is an error (this is so
+##'   that `pack()` is not broken).  We will likely play around with
+##'   this process in future in order to get automatic differentiation
+##'   to work.
+##'
 ##' @inheritParams monty_packer
 ##'
 ##' @return An object of class `monty_packer_grouped`, which has the
@@ -96,9 +106,12 @@ monty_packer_grouped <- function(groups, scalar = NULL, array = NULL,
     cli::cli_abort("Expected at least two groups", arg = "groups")
   }
   if (!is.null(process)) {
-    cli::cli_abort("'process' is not yet compatible with grouped packers")
+    if (!is.function(process)) {
+      cli::cli_abort(
+        "Expected a function for 'process'",
+        arg = "process")
+    }
   }
-
   if (!is.null(fixed)) {
     i <- names(fixed) %in% groups
     fixed <- list(shared = if (!all(i)) fixed[!i],
@@ -186,6 +199,9 @@ monty_packer_grouped <- function(groups, scalar = NULL, array = NULL,
       if (!is.null(fixed$varied)) {
         ret[[i]][names(fixed$varied[[i]])] <- fixed$varied[[i]]
       }
+      if (!is.null(process)) {
+        ret[[i]] <- unpack_vector_process(ret[[i]], process)
+      }
     }
     names(ret) <- groups
     ret

R/packer.R

@@ -651,3 +651,19 @@ pack_check_dimensions <- function(p, shape, fixed, process,
 
   ret
 }
+
+
+unpack_vector_process <- function(x, process) {
+  extra <- process(x)
+  err <- intersect(names(extra), names(x))
+  if (length(err) > 0) {
+    cli::cli_abort(
+      c("'process()' is trying to overwrite entries in your list",
+        i = paste("The 'process()' function should only create elements",
+                  "that are not already present in 'scalar', 'array'",
+                  "or 'fixed', as this lets us reverse the transformation",
+                  "process"),
+        x = "{?Entry/Entries} already present: {squote(err)}"))
+  }
+  c(x, extra)
+}

tests/testthat/test-packer-grouped.R

@@ -155,13 +155,6 @@ test_that("prevent varied names in fixed clashing with elements in packer", {
 })
 
 
-test_that("can't use 'progress' with a grouped packer", {
-  expect_error(
-    monty_packer_grouped(c("x", "y"), c("a", "b"), process = identity),
-    "process' is not yet compatible with grouped packers")
-})
-
-
 test_that("grouped packers require at least two groups", {
   expect_error(
     monty_packer_grouped("x", c("a", "b")),
@@ -237,3 +230,14 @@ test_that("Can print a grouped packer", {
                "Packing 4 values: 'x<a>', 'y<a>', 'x<b>', and 'y<b>",
                fixed = TRUE, all = FALSE)
 })
+
+
+test_that("can used process with grouped packer", {
+  process <- function(res) {
+    list(z = res$x + res$y)
+  }
+  p <- monty_packer_grouped(c("a", "b"), c("x", "y"), process = process)
+  expect_equal(p$unpack(1:4),
+               list(a = list(x = 1, y = 2, z = 3),
+                    b = list(x = 3, y = 4, z = 7)))
+})