From da981646c10e303dec81e15bd92c989a94a7deb9 Mon Sep 17 00:00:00 2001
From: Daniel <mail@danielluedecke.de>
Date: Mon, 4 Mar 2024 08:22:49 +0100
Subject: [PATCH] allow n()

---
 R/data_modify.R                    | 8 +++++++-
 R/data_summary.R                   | 3 +++
 man/data_summary.Rd                | 3 +++
 tests/testthat/test-data_summary.R | 8 ++++++++
 4 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/R/data_modify.R b/R/data_modify.R
index 6234255fd..bf85ff045 100644
--- a/R/data_modify.R
+++ b/R/data_modify.R
@@ -350,7 +350,13 @@ data_modify.grouped_df <- function(data, ..., .if = NULL, .at = NULL, .modify =
   }
 
   # finally, we can evaluate expression and get values for new variables
-  new_variable <- try(with(data, eval(symbol)), silent = TRUE)
+  new_variable <- switch(
+    insight::safe_deparse(symbol),
+    # "special" functions
+    "n()" = nrow(data),
+    # default evaluation of expression
+    try(with(data, eval(symbol)), silent = TRUE)
+  )
 
   # successful, or any errors, like misspelled variable name?
   if (inherits(new_variable, "try-error")) {
diff --git a/R/data_summary.R b/R/data_summary.R
index 90f3e8ae3..65540da88 100644
--- a/R/data_summary.R
+++ b/R/data_summary.R
@@ -38,6 +38,9 @@
 #'
 #' # expressions can also be supplied as character strings
 #' data_summary(mtcars, "MW = mean(mpg)", "SD = sd(mpg)", by = c("am", "gear"))
+#'
+#' # count observations within groups
+#' data_summary(mtcars, observations = n(), by = c("am", "gear"))
 #' @export
 data_summary <- function(x, ...) {
   UseMethod("data_summary")
diff --git a/man/data_summary.Rd b/man/data_summary.Rd
index 0602dc7da..01fefae8c 100644
--- a/man/data_summary.Rd
+++ b/man/data_summary.Rd
@@ -52,4 +52,7 @@ data_summary(mtcars, MW = mean(mpg), SD = sd(mpg), by = c("am", "gear"))
 
 # expressions can also be supplied as character strings
 data_summary(mtcars, "MW = mean(mpg)", "SD = sd(mpg)", by = c("am", "gear"))
+
+# count observations within groups
+data_summary(mtcars, observations = n(), by = c("am", "gear"))
 }
diff --git a/tests/testthat/test-data_summary.R b/tests/testthat/test-data_summary.R
index aede5c042..2f7fd3308 100644
--- a/tests/testthat/test-data_summary.R
+++ b/tests/testthat/test-data_summary.R
@@ -200,3 +200,11 @@ test_that("data_summary, expression as variable", {
   expect_named(out, c("am", "gear", "MW", "SD"))
   expect_equal(out$SD, aggregate(mtcars["mpg"], list(mtcars$am, mtcars$gear), sd)$mpg, tolerance = 1e-4)
 })
+
+
+test_that("data_summary, extra functions", {
+  data(mtcars)
+  # n()
+  out <- data_summary(mtcars, n = n(), by = c("am", "gear"))
+  expect_identical(out$n, c(15L, 4L, 8L, 5L))
+})