add sparse argument to step_dummy()

NEWS.md

@@ -10,6 +10,8 @@
 
 * All steps and checks now require arguments `trained`, `skip`, `role`, and `id` at all times.
 
+* `step_dummy()` gained `sparse` argument. When set to `TRUE`, `step_dummy()` will produce sparse vectors. (#1392)
+
 # recipes 1.1.0
 
 ## Improvements

R/dummy.R

@@ -18,6 +18,9 @@
 #' @param levels A list that contains the information needed to create dummy
 #'   variables for each variable contained in `terms`. This is `NULL` until the
 #'   step is trained by [prep()].
+#' @param sparse A logical. Should the columns produced be sparse vectors.
+#'   Sparsity is only supported for `"contr.treatment"` contrasts. Defaults to 
+#'   `FALSE`.
 #' @template step-return
 #' @family dummy variable and encoding steps
 #' @seealso [dummy_names()]
@@ -60,7 +63,8 @@
 #' this step.
 #'
 #' Also, there are a number of contrast methods that return fractional values.
-#' The columns returned by this step are doubles (not integers).
+#' The columns returned by this step are doubles (not integers) when 
+#' `sparse = FALSE`. The columns returned when `sparse = TRUE` are integers.
 #'
 #' The [package vignette for dummy variables](https://recipes.tidymodels.org/articles/Dummies.html)
 #' and interactions has more information.
@@ -121,6 +125,7 @@
            preserve = deprecated(),
            naming = dummy_names,
            levels = NULL,
+           sparse = FALSE,
            keep_original_cols = FALSE,
            skip = FALSE,
            id = rand_id("dummy")) {
@@ -143,6 +148,7 @@
         preserve = keep_original_cols,
         naming = naming,
         levels = levels,
+        sparse = sparse,
         keep_original_cols = keep_original_cols,
         skip = skip,
         id = id
@@ -151,7 +157,7 @@
   }
 
 step_dummy_new <-
-  function(terms, role, trained, one_hot, preserve, naming, levels,
+  function(terms, role, trained, one_hot, preserve, naming, levels, sparse,
            keep_original_cols, skip, id) {
     step(
       subclass = "dummy",
@@ -162,6 +168,7 @@
       preserve = preserve,
       naming = naming,
       levels = levels,
+      sparse = sparse,
       keep_original_cols = keep_original_cols,
       skip = skip,
       id = id
@@ -174,6 +181,7 @@
   check_type(training[, col_names], types = c("factor", "ordered"))
   check_bool(x$one_hot, arg = "one_hot")
   check_function(x$naming, arg = "naming", allow_empty = FALSE)
+  check_bool(x$sparse, arg = "sparse")
 
   if (length(col_names) > 0) {
     ## I hate doing this but currently we are going to have
@@ -218,6 +226,7 @@
     preserve = x$preserve,
     naming = x$naming,
     levels = levels,
+    sparse = x$sparse,
     keep_original_cols = get_keep_original_cols(x),
     skip = x$skip,
     id = x$id
@@ -285,43 +294,60 @@
       col_name,
       step = "step_dummy"
     )
+
+    new_data[, col_name] <- factor(
+      new_data[[col_name]],
+      levels = levels_values,
+      ordered = is_ordered
+    )
 
-    new_data[, col_name] <-
-      factor(
-        new_data[[col_name]],
-        levels = levels_values,
-        ordered = is_ordered
-      )
+    if (object$sparse) {
+      current_contrast <- getOption("contrasts")[is_ordered + 1]
+      if (current_contrast != "contr.treatment") {
+        cli::cli_abort(
+          "When {.code sparse = TRUE}, only {.val contr.treatment} contrasts are
+          supported, not {.val {current_contrast}}."
+        )
+      } 
 
-    indicators <-
-      model.frame(
-        rlang::new_formula(lhs = NULL, rhs = rlang::sym(col_name)),
-        data = new_data[, col_name],
-        xlev = levels_values,
-        na.action = na.pass
+      indicators <- sparsevctrs::sparse_dummy(
+        x = new_data[[col_name]],
+        one_hot = object$one_hot
       )
-
-    indicators <- tryCatch(
-      model.matrix(object = levels, data = indicators),
-      error = function(cnd) {
-        if (grepl("(vector memory|cannot allocate)", cnd$message)) {
-          n_levels <- length(attr(levels, "values"))
-          cli::cli_abort(
-            "{.var {col_name}} contains too many levels ({n_levels}), \\
-            which would result in a data.frame too large to fit in memory.",
-            call = NULL
-          )
+      indicators <- tibble::new_tibble(indicators)
+      used_lvl <- colnames(indicators)
+    } else {
+      indicators <-
+        model.frame(
+          rlang::new_formula(lhs = NULL, rhs = rlang::sym(col_name)),
+          data = new_data[, col_name],
+          xlev = levels_values,
+          na.action = na.pass
+        )
+
+      indicators <- tryCatch(
+        model.matrix(object = levels, data = indicators),
+        error = function(cnd) {
+          if (grepl("(vector memory|cannot allocate)", cnd$message)) {
+            n_levels <- length(attr(levels, "values"))
+            cli::cli_abort(
+              "{.var {col_name}} contains too many levels ({n_levels}), \\
+              which would result in a data.frame too large to fit in memory.",
+              call = NULL
+            )
+          }
+          stop(cnd)
         }
-        stop(cnd)
+      )
+
+      if (!object$one_hot) {
+        indicators <- indicators[, colnames(indicators) != "(Intercept)", drop = FALSE]
       }
-    )
-
-    if (!object$one_hot) {
-      indicators <- indicators[, colnames(indicators) != "(Intercept)", drop = FALSE]
+
+      ## use backticks for nonstandard factor levels here
+      used_lvl <- gsub(paste0("^\\`?", col_name, "\\`?"), "", colnames(indicators))
     }
-
-    ## use backticks for nonstandard factor levels here
-    used_lvl <- gsub(paste0("^\\`?", col_name, "\\`?"), "", colnames(indicators))
+
     new_names <- object$naming(col_name, used_lvl, is_ordered)
     colnames(indicators) <- new_names
     indicators <- check_name(indicators, new_data, object, new_names)

tests/testthat/_snaps/dummy.md

@@ -154,6 +154,16 @@
       Caused by error in `bake()`:
       ! Only one factor level in `x`: "only-level".
 
+# sparse = TRUE errors on unsupported contrasts
+
+    Code
+      recipe(~., data = tibble(x = letters)) %>% step_dummy(x, sparse = TRUE) %>%
+        prep()
+    Condition
+      Error in `step_dummy()`:
+      Caused by error in `bake()`:
+      ! When `sparse = TRUE`, only "contr.treatment" contrasts are supported, not "contr.helmert".
+
 # bake method errors when needed non-standard role columns are missing
 
     Code

tests/testthat/test-dummy.R

@@ -354,6 +354,34 @@ test_that("throws an informative error for single level", {
   )
 })
 
+test_that("sparse = TRUE works", {
+  rec <- recipe(~ ., data = tibble(x = c(NA, letters)))
+
+  suppressWarnings({
+    dense <- rec %>% step_dummy(x, sparse = FALSE) %>% prep() %>% bake(NULL)
+    dense <- purrr::map(dense, as.integer) %>% tibble::new_tibble()
+    sparse <- rec %>% step_dummy(x, sparse = TRUE) %>% prep() %>% bake(NULL)
+  })
+
+  expect_identical(dense, sparse)
+
+  expect_false(any(vapply(dense, sparsevctrs::is_sparse_vector, logical(1))))
+  expect_true(all(vapply(sparse, sparsevctrs::is_sparse_vector, logical(1))))
+})
+
+test_that("sparse = TRUE errors on unsupported contrasts", {
+  go_helmert <- getOption("contrasts")
+  go_helmert["unordered"] <- "contr.helmert"
+  withr::local_options(contrasts = go_helmert)
+
+  expect_snapshot(
+    error = TRUE,
+    recipe(~ ., data = tibble(x = letters)) %>% 
+      step_dummy(x, sparse = TRUE) %>% 
+      prep()
+  )
+})
+
 # Infrastructure ---------------------------------------------------------------
 
 test_that("bake method errors when needed non-standard role columns are missing", {