Merge branch 'f-#99-add-column'

- New `add_column()`, analogously to `add_row()` (#99).

NAMESPACE

@@ -52,6 +52,7 @@ S3method(type_sum,difftime)
 S3method(type_sum,factor)
 S3method(type_sum,ordered)
 S3method(type_sum,tbl_df)
+export(add_column)
 export(add_row)
 export(as_data_frame)
 export(as_tibble)

R/dataframe.R

@@ -276,6 +276,7 @@ is_tibble <- is.tibble
 #' @param .data Data frame to append to.
 #' @param ... Name-value pairs. If you don't supply the name of a variable,
 #'   it'll be given the value \code{NA}.
+#' @family addition
 #' @examples
 #' # add_row ---------------------------------
 #' df <- tibble(x = 1:3, y = 3:1)
@@ -312,6 +313,52 @@ add_row <- function(.data, ...) {
   rbind(.data, df)
 }
 
+#' Add columns to a data frame
+#'
+#' This is a convenient way to add one or more columns to an existing data
+#' frame.
+#'
+#' @param .data Data frame to append to.
+#' @param ... Name-value pairs, all values must have one element for each row
+#'   in the data frame, or be of length 1
+#' @family addition
+#' @examples
+#' # add_row ---------------------------------
+#' df <- tibble(x = 1:3, y = 3:1)
+#'
+#' add_column(df, z = -1:1, w = 0)
+#'
+#' # You can't overwrite existing columns
+#' \dontrun{
+#' add_column(df, x = 4:6)
+#' }
+
+#' # You can't create new observations
+#' \dontrun{
+#' add_column(df, z = 1:5)
+#' }
+#' @export
+add_column <- function(.data, ...) {
+  df <- tibble(...)
+
+  if (ncol(df) == 0L) {
+    return(.data)
+  }
+
+  if (nrow(df) != nrow(.data)) {
+    stopc("Expected ", nrow(.data), " rows, got ", nrow(df))
+  }
+
+  extra_vars <- intersect(names(df), names(.data))
+  if (length(extra_vars) > 0) {
+    stopc(
+      "Columns already in data frame: ", format_n(extra_vars)
+    )
+  }
+
+  structure(cbind(.data, df), class = class(.data))
+}
+
 # Validity checks --------------------------------------------------------------
 
 check_tibble <- function(x) {

tests/testthat/test-data_frame.R

@@ -213,17 +213,22 @@ test_that("names must be unique (#820)", {
 
 test_that("can add new row", {
   df_all_new <- add_row(df_all, a = 4, b = 3L)
+  expect_identical(colnames(df_all_new), colnames(df_all))
   expect_identical(nrow(df_all_new), nrow(df_all) + 1L)
   expect_identical(df_all_new$a, c(df_all$a, 4))
   expect_identical(df_all_new$b, c(df_all$b, 3L))
   expect_identical(df_all_new$c, c(df_all$c, NA))
+})
 
+test_that("add_row() keeps class of object", {
   iris_new <- add_row(iris, Species = "unknown")
   expect_equal(class(iris), class(iris_new))
 
   iris_new <- add_row(as_tibble(iris), Species = "unknown")
   expect_equal(class(as_tibble(iris)), class(iris_new))
+})
 
+test_that("adds empty row if no arguments", {
   new_iris_row <- add_row(iris)[nrow(iris) + 1, , drop = TRUE]
   expect_true(all(is.na(new_iris_row)))
 })
@@ -247,3 +252,51 @@ test_that("can recycle when adding rows", {
   expect_identical(as.character(iris_new$Species),
                    c(as.character(iris$Species), "unknown", "unknown"))
 })
+
+# add_column ------------------------------------------------------------
+
+test_that("can add new column", {
+  df_all_new <- add_column(df_all, j = 1:3, k = 3:1)
+  expect_identical(nrow(df_all_new), nrow(df_all))
+  expect_identical(df_all_new[seq_along(df_all)], df_all)
+  expect_identical(df_all_new$j, 1:3)
+  expect_identical(df_all_new$k, 3:1)
+})
+
+test_that("add_column() keeps class of object", {
+  iris_new <- add_column(iris, x = 1:150)
+  expect_equal(class(iris), class(iris_new))
+
+  iris_new <- add_column(as_tibble(iris), x = 1:150)
+  expect_equal(class(as_tibble(iris)), class(iris_new))
+})
+
+test_that("add_column() keeps unchanged if no arguments", {
+  expect_identical(iris, add_column(iris))
+})
+
+test_that("error if adding existing columns", {
+  expect_error(add_column(tibble(a = 3), a = 5),
+               "Columns already in data frame")
+})
+
+test_that("error if adding wrong number of rows with add_column()", {
+  expect_error(add_column(tibble(a = 3), b = 4:5),
+               "Expected 1 rows, got 2")
+})
+
+test_that("can add multiple columns", {
+  df <- tibble(a = 1:3)
+  df_new <- add_column(df, b = 4:6, c = 3:1)
+  expect_identical(ncol(df_new), ncol(df) + 2L)
+  expect_identical(df_new$b, 4:6)
+  expect_identical(df_new$c, 3:1)
+})
+
+test_that("can recycle when adding columns", {
+  df <- tibble(a = 1:3)
+  df_new <- add_column(df, b = 4, c = 3:1)
+  expect_identical(ncol(df_new), ncol(df) + 2L)
+  expect_identical(df_new$b, rep(4, 3))
+  expect_identical(df_new$c, 3:1)
+})