albertlockett commented on code in PR #7611:
URL: https://github.com/apache/arrow-rs/pull/7611#discussion_r2145389529
##########
arrow-array/src/builder/generic_bytes_dictionary_builder.rs:
##########
@@ -152,6 +155,65 @@ where
values_builder,
})
}
+
+ /// Creates a new `GenericByteDictionaryBuilder` from the existing builder
with the same
+ /// keys and values, but with a new data type for the keys.
+ ///
+ /// # example
+ /// ```
+ /// # use arrow_array::builder::StringDictionaryBuilder;
+ /// # use arrow_array::types::{UInt8Type, UInt16Type};
+ /// # use arrow_array::UInt16Array;;
+ ///
+ /// let mut u8_keyed_builder = StringDictionaryBuilder::<UInt8Type>::new();
+ /// u8_keyed_builder.append("def").unwrap();
+ /// u8_keyed_builder.append_null();
+ /// u8_keyed_builder.append("abc").unwrap();
+ ///
+ /// // for some reason, we decide we need to upgrade the key type
+ /// let mut u16_keyed_builder =
StringDictionaryBuilder::<UInt16Type>::try_new_from_builder(u8_keyed_builder).unwrap();
+ /// let dictionary_array = u16_keyed_builder.finish();
+ /// let keys = dictionary_array.keys();
+ ///
+ /// assert_eq!(keys, &UInt16Array::from(vec![Some(0), None, Some(1)]));
+ /// ```
+ pub fn try_new_from_builder<K2>(
+ mut source: GenericByteDictionaryBuilder<K2, T>,
+ ) -> Result<Self, ArrowError>
+ where
+ K::Native: NumCast,
+ K2: ArrowDictionaryKeyType,
+ K2::Native: NumCast,
+ {
+ let state = source.state;
+ let dedup = source.dedup;
+ let values_builder = source.values_builder;
+
+ let source_keys = source.keys_builder.finish();
+ let new_keys: PrimitiveArray<K> = source_keys.try_unary(|value| {
+ num::cast::cast::<K2::Native, K::Native>(value).ok_or_else(|| {
Review Comment:
Thanks Andrew!
Created a follow up issue for this
https://github.com/apache/arrow-rs/issues/7662 . You can assign this to me as
well.
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