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GH-39603: [R] Error: Cannot convert Dictionary Array of type dictionary<values=large_string, indices=uint32, ordered=0> to R #49710

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Merged
thisisnic merged 7 commits into from
Jun 10, 2026
+36 −12
Merged

GH-39603: [R] Error: Cannot convert Dictionary Array of type dictionary<values=large_string, indices=uint32, ordered=0> to R #49710

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a0fb656
Allow dictionaries from a wider range of types for indices
thisisnic Apr 11, 2026
80788ae
Apply suggestion from @thisisnic
thisisnic Jun 8, 2026
1e02dcb
add coilot suggested test
thisisnic Jun 8, 2026
bfcc9c6
Combine tests
thisisnic Jun 8, 2026
3f57394
Account for large strings
thisisnic Jun 10, 2026
0661910
don't forget the large ones
thisisnic Jun 10, 2026
bc33f7c
don't hardcode levels
thisisnic Jun 10, 2026
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2 changes: 2 additions & 0 deletions cpp/src/arrow/util/converter.h
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Original file line number Diff line number Diff line change
Expand Up @@ -238,7 +238,9 @@ struct MakeConverterImpl {
DICTIONARY_CASE(FloatType);
DICTIONARY_CASE(DoubleType);
DICTIONARY_CASE(BinaryType);
DICTIONARY_CASE(LargeBinaryType);
DICTIONARY_CASE(StringType);
DICTIONARY_CASE(LargeStringType);
DICTIONARY_CASE(FixedSizeBinaryType);
#undef DICTIONARY_CASE
default:
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26 changes: 24 additions & 2 deletions r/src/array_to_vector.cpp
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Expand Up @@ -595,7 +595,9 @@ class Converter_Dictionary : public Converter {
case Type::UINT16:
case Type::INT16:
case Type::INT32:
// TODO: also add int64, uint32, uint64 downcasts, if possible
case Type::UINT32:
case Type::INT64:
case Type::UINT64:
break;
default:
cpp11::stop("Cannot convert Dictionary Array of type `%s` to R",
Expand All @@ -612,6 +614,16 @@ class Converter_Dictionary : public Converter {
dictionary_ = CreateEmptyArray(dict_type.value_type());
}
}

// R factors store their codes in 32-bit integers, so dictionary arrays with
// more levels than that cannot be represented safely.
if (dictionary_->length() > std::numeric_limits<int>::max()) {
const auto& dict_type = checked_cast<const DictionaryType&>(*chunked_array->type());
cpp11::stop(
"Cannot convert Dictionary Array of type `%s` to R: dictionary has "
"more levels than an R factor can represent",
dict_type.ToString().c_str());
}
}

SEXP Allocate(R_xlen_t n) const {
Expand Down Expand Up @@ -653,6 +665,15 @@ class Converter_Dictionary : public Converter {
case Type::INT32:
return Ingest_some_nulls_Impl<arrow::Int32Type>(data, array, start, n,
chunk_index);
case Type::UINT32:
return Ingest_some_nulls_Impl<arrow::UInt32Type>(data, array, start, n,
chunk_index);
case Type::INT64:
return Ingest_some_nulls_Impl<arrow::Int64Type>(data, array, start, n,
chunk_index);
case Type::UINT64:
return Ingest_some_nulls_Impl<arrow::UInt64Type>(data, array, start, n,
chunk_index);
default:
break;
}
Expand Down Expand Up @@ -704,7 +725,8 @@ class Converter_Dictionary : public Converter {
// TODO (npr): this coercion should be optional, "dictionariesAsFactors" ;)
// Alternative: preserve the logical type of the dictionary values
// (e.g. if dict is timestamp, return a POSIXt R vector, not factor)
if (dictionary_->type_id() != Type::STRING) {
if (dictionary_->type_id() != Type::STRING &&
dictionary_->type_id() != Type::LARGE_STRING) {
cpp11::safe[Rf_warning]("Coercing dictionary values to R character factor levels");
}

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4 changes: 2 additions & 2 deletions r/src/r_to_arrow.cpp
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Expand Up @@ -1029,8 +1029,8 @@ class RDictionaryConverter<ValueType, enable_if_has_string_view<ValueType>>

// first we need to handle the levels
SEXP levels = Rf_getAttrib(x, R_LevelsSymbol);
auto memo_chunked_chunked_array =
arrow::r::vec_to_arrow_ChunkedArray(levels, utf8(), false);
auto memo_chunked_chunked_array = arrow::r::vec_to_arrow_ChunkedArray(
levels, this->dict_type_->value_type(), false);
for (const auto& chunk : memo_chunked_chunked_array->chunks()) {
RETURN_NOT_OK(this->value_builder_->InsertMemoValues(*chunk));
}
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16 changes: 8 additions & 8 deletions r/tests/testthat/test-Table.R
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Expand Up @@ -357,18 +357,18 @@ test_that("Table handles null type (ARROW-7064)", {

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()) # nolint
for (i in int_types) {
index_types <- c(int8(), int16(), int32(), int64(), uint8(), uint16(), uint32(), uint64())
for (i in index_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_equal_data_frame(tab, fact)
}
expect_equal_data_frame(tab, fact)
}

# large_utf8 values exercise the non-ALTREP conversion path
tab_large <- Table$create(fact, schema = schema(fct = dictionary(uint32(), large_utf8())))
expect_equal(tab_large$schema, schema(fct = dictionary(uint32(), large_utf8())))
expect_equal_data_frame(tab_large, fact)
})

test_that("Table unifies dictionary on conversion back to R (ARROW-8374)", {
Expand Down
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