comments

R/data_modify.R

@@ -149,6 +149,11 @@ data_modify.default <- function(data, ...) {
 data_modify.data.frame <- function(data, ..., .if = NULL, .at = NULL, .modify = NULL) {
   dots <- eval(substitute(alist(...)))
 
+  # error for data frames with no rows...
+  if (nrow(data) == 0) {
+    insight::format_error("`data_modify()` only works for data frames with at least one row.")
+  }
+
   # check if we have dots, or only at/modify ----
 
   if (length(dots)) {
@@ -205,6 +210,10 @@ data_modify.grouped_df <- function(data, ..., .if = NULL, .at = NULL, .modify =
   # the data.frame method later...
   dots <- match.call(expand.dots = FALSE)[["..."]]
 
+  # error for data frames with no rows...
+  if (nrow(data) == 0) {
+    insight::format_error("`data_modify()` only works for data frames with at least one row.")
+  }
 
   grps <- attr(data, "groups", exact = TRUE)
   grps <- grps[[".rows"]]
@@ -358,8 +367,8 @@ data_modify.grouped_df <- function(data, ..., .if = NULL, .at = NULL, .modify =
   if (!is.null(symbol_string) && all(symbol_string == "n()")) {
     # "special" functions - using "n()" just returns number of rows
     new_variable <- nrow(data)
-  } else if (!is.null(symbol_string) && length(symbol_string) == 1 && grepl("n()", symbol_string, fixed = TRUE)) {
-    # "special" functions, like "1:n()" or similar
+  } else if (!is.null(symbol_string) && length(symbol_string) == 1 && grepl("\\bn\\(\\)", symbol_string)) {
+    # "special" functions, like "1:n()" or similar - but not "1:fun()"
     symbol_string <- str2lang(gsub("n()", "nrow(data)", symbol_string, fixed = TRUE))
     new_variable <- try(with(data, eval(symbol_string)), silent = TRUE)
   } else {

tests/testthat/test-data_modify.R

@@ -353,6 +353,13 @@ test_that("data_modify errors for non df", {
 })
 
 
+test_that("data_modify errors for empty data frames", {
+  data(mtcars)
+  x <- mtcars[1, ]
+  expect_error(data_modify(x[-1, ], new_var = 5), regex = "`data_modify()` only works")
+})
+
+
 test_that("data_modify errors for non df", {
   data(efc)
   a <- "center(c22hour)" # <---------------- error in variable name
@@ -492,8 +499,10 @@ test_that("data_modify works with functions that return character vectors", {
 })
 
 
-test_that("data_modify 1:n() and similar works in grouped data frames", {
+test_that("data_modify 1:n() and similar works in (grouped) data frames", {
   data(mtcars)
+  out <- data_modify(mtcars, Trials = 1:n()) # nolint
+  expect_identical(out$Trials, 1:32)
   x <- data_group(mtcars, "gear")
   out <- data_modify(x, Trials = 1:n()) # nolint
   expect_identical(out$Trials[out$gear == 3], 1:15)
@@ -562,3 +571,27 @@ test_that("data_modify .if/.at arguments", {
   out <- data_modify(d, new_length = Petal.Length * 2, .if = is.numeric, .modify = round)
   expect_equal(out$new_length, c(3, 3, 3, 3, 3), ignore_attr = TRUE)
 })
+
+
+skip_if_not_installed("withr")
+
+withr::with_environment(
+  new.env(),
+  test_that("data_modify 1:n() and similar works in (grouped) data frames inside function calls", {
+    data(mtcars)
+    x <- data_group(mtcars, "gear")
+
+    foo <- function(d) {
+      out <- data_modify(d, Trials = 1:n())
+      out$Trials
+    }
+    expect_identical(
+      foo(x),
+      c(
+        1L, 2L, 3L, 1L, 2L, 3L, 4L, 4L, 5L, 6L, 7L, 5L, 6L, 7L, 8L,
+        9L, 10L, 8L, 9L, 10L, 11L, 12L, 13L, 14L, 15L, 11L, 1L, 2L, 3L,
+        4L, 5L, 12L
+      )
+    )
+  })
+)