jhorstmann commented on code in PR #6383:
URL: https://github.com/apache/arrow-rs/pull/6383#discussion_r1758773588
##########
arrow-cast/src/cast/dictionary.rs:
##########
@@ -203,10 +203,36 @@ pub(crate) fn cast_to_dictionary<K:
ArrowDictionaryKeyType>(
UInt32 => pack_numeric_to_dictionary::<K, UInt32Type>(array,
dict_value_type, cast_options),
UInt64 => pack_numeric_to_dictionary::<K, UInt64Type>(array,
dict_value_type, cast_options),
Decimal128(_, _) => {
- pack_numeric_to_dictionary::<K, Decimal128Type>(array,
dict_value_type, cast_options)
+ // pack_numeric_to_dictionary loses the precision and scale so we
have to perform a
+ // second cast
+ let decimal_dict_max_precision_scale =
pack_numeric_to_dictionary::<K, Decimal128Type>(
Review Comment:
The `PrimitiveDictionaryBuilder` used during casting seems to already loose
the custom precision and scale. Its `new` or `with_capacity` methods use the
default data type of the generic `ArrowPrimitiveType`. Maybe adding a
`with_capacity_and_data_type` method that calls `values_builder.with_data_type`
could be a more general fix.
https://github.com/apache/arrow-rs/blob/53.0.0/arrow-array/src/builder/primitive_builder.rs#L152
https://github.com/apache/arrow-rs/blob/53.0.0/arrow-cast/src/cast/dictionary.rs#L299
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