Resolves tidyverse#171

When add_row to an empty tibble, all column classes were converted to logical.

We fix this by checking whether we're adding to an empty tibble. If yes, we coerce column classes back to the original.

R/RcppExports.R

@@ -1,4 +1,4 @@
-# This file was generated by Rcpp::compileAttributes
+# Generated by using Rcpp::compileAttributes() -> do not edit by hand
 # Generator token: 10BE3573-1514-4C36-9D1C-5A225CD40393
 
 matrixToDataFrame <- function(x) {

R/add.R

@@ -57,6 +57,17 @@ add_row <- function(.data, ..., .before = NULL, .after = NULL) {
     out <- rbind(.data[indexes, ], df, .data[-indexes, ])
   }
 
+  # If .data is empty, coerce the out column class to .data class
+  if (nrow(.data) == 0) {
+    for (i in 1:ncol(out)) {
+      if (class(.data[[i]])[1] == "factor") {
+        out[[i]] <- as.factor(NA)
+      } else {
+        class(out[[i]]) <- class(.data[[i]])
+      }
+    }
+  }
+
   set_class(remove_rownames(out), class(.data))
 }
 

src/RcppExports.cpp

@@ -1,4 +1,4 @@
-// This file was generated by Rcpp::compileAttributes
+// Generated by using Rcpp::compileAttributes() -> do not edit by hand
 // Generator token: 10BE3573-1514-4C36-9D1C-5A225CD40393
 
 #include <Rcpp.h>
@@ -9,10 +9,10 @@ using namespace Rcpp;
 List matrixToDataFrame(SEXP x);
 RcppExport SEXP tibble_matrixToDataFrame(SEXP xSEXP) {
 BEGIN_RCPP
-    Rcpp::RObject __result;
-    Rcpp::RNGScope __rngScope;
+    Rcpp::RObject rcpp_result_gen;
+    Rcpp::RNGScope rcpp_rngScope_gen;
     Rcpp::traits::input_parameter< SEXP >::type x(xSEXP);
-    __result = Rcpp::wrap(matrixToDataFrame(x));
-    return __result;
+    rcpp_result_gen = Rcpp::wrap(matrixToDataFrame(x));
+    return rcpp_result_gen;
 END_RCPP
 }

tests/testthat/helper-data.R

@@ -10,3 +10,17 @@ df_all <- tibble(
   h = as.list(c(1:2, NA)),
   i = list(list(1, 2:3), list(4:6), list(NA))
 )
+
+# An empty data frame with all major types
+df_empty = tibble(
+  a = integer(0),
+  b = double(0),
+  c = logical(0),
+  d = character(0),
+  e = factor(integer(0)),
+  f = as.Date(character(0)),
+  g = as.POSIXct(character(0)),
+  h = as.list(double(0)),
+  # i = list(list(integer(0)), list(character(0))),
+  to_be_added = double(0)
+)

tests/testthat/test-add.R

@@ -96,6 +96,11 @@ test_that("adding to a list column adds a NULL value (#148)", {
   expect_null(add_row(data_frame(a = as.list(1:3), b = 1:3), b = 4:6)$a[[5]])
 })
 
+test_that("add_row() keeps the class of empty columns", {
+  new_tibble <- add_row(df_empty, to_be_added = 5)
+  expect_equal(sapply(df_empty, class), sapply(new_tibble, class))
+})
+
 # add_column ------------------------------------------------------------
 
 test_that("can add new column", {