ARROW-8977: [R] Table$create with schema crashes with some dictionary index types

r/src/array_from_vector.cpp

@@ -351,14 +351,19 @@ std::shared_ptr<Array> MakeFactorArrayImpl(Rcpp::IntegerVector_ factor,
 
 std::shared_ptr<Array> MakeFactorArray(Rcpp::IntegerVector_ factor,
                                        const std::shared_ptr<arrow::DataType>& type) {
-  SEXP levels = factor.attr("levels");
-  int n = Rf_length(levels);
-  if (n < 128) {
-    return MakeFactorArrayImpl<arrow::Int8Type>(factor, type);
-  } else if (n < 32768) {
-    return MakeFactorArrayImpl<arrow::Int16Type>(factor, type);
-  } else {
-    return MakeFactorArrayImpl<arrow::Int32Type>(factor, type);
+  const auto& dict_type = checked_cast<const arrow::DictionaryType&>(*type);
+  switch (dict_type.index_type()->id()) {
+    case Type::INT8:
+      return MakeFactorArrayImpl<arrow::Int8Type>(factor, type);
+    case Type::INT16:
+      return MakeFactorArrayImpl<arrow::Int16Type>(factor, type);
+    case Type::INT32:
+      return MakeFactorArrayImpl<arrow::Int32Type>(factor, type);
+    case Type::INT64:
+      return MakeFactorArrayImpl<arrow::Int64Type>(factor, type);
+    default:
+      Rcpp::stop(tfm::format("Cannot convert to dictionary with index_type %s",
+                             dict_type.index_type()->ToString()));
   }
 }
 
@@ -1297,8 +1302,8 @@ bool CheckCompatibleFactor(SEXP obj, const std::shared_ptr<arrow::DataType>& typ
     return false;
   }
 
-  auto* dict_type = checked_cast<arrow::DictionaryType*>(type.get());
-  return dict_type->value_type()->Equals(utf8());
+  const auto& dict_type = checked_cast<const arrow::DictionaryType&>(*type);
+  return dict_type.value_type()->Equals(utf8());
 }
 
 arrow::Status CheckCompatibleStruct(SEXP obj,

r/src/array_to_vector.cpp

@@ -357,6 +357,7 @@ class Converter_Dictionary : public Converter {
       case Type::UINT16:
       case Type::INT16:
       case Type::INT32:
+        // TODO: also add int64, uint32, uint64 downcasts, if possible
         break;
       default:
         Rcpp::stop("Cannot convert Dictionary Array of type `%s` to R",

r/tests/testthat/test-Table.R

@@ -321,3 +321,19 @@ test_that("Table handles null type (ARROW-7064)", {
   tab <- Table$create(a = 1:10, n = vctrs::unspecified(10))
   expect_equivalent(tab$schema, schema(a = int32(), n = null()))
 })
+
+test_that("Can create table with specific dictionary types", {
+  fact <- example_data[,"fct"]
+  int_types <- c(int8(), int16(), int32(), int64())
+  # TODO: test uint types when format allows
+  # uint_types <- c(uint8(), uint16(), uint32(), uint64())
+  for (i in int_types) {
+    sch <- schema(fct = dictionary(i, utf8()))
+    tab <- Table$create(fact, schema = sch)
+    expect_equal(sch, tab$schema)
+    if (i != int64()) {
+      # TODO: same downcast to int32 as we do for int64() type elsewhere
+      expect_identical(as.data.frame(tab), fact)
+    }
+  }
+})