From 82e3b8d77ae5820dd3bcb090649fe00ca0babfae Mon Sep 17 00:00:00 2001
From: Liang-Chi Hsieh <viirya@gmail.com>
Date: Wed, 4 Jan 2023 09:37:20 -0800
Subject: [PATCH] Support casting from binary to dictionary of binary

---
 arrow-cast/src/cast.rs    | 26 ++++++++++++++++++++++++++
 arrow/tests/array_cast.rs |  2 ++
 2 files changed, 28 insertions(+)

diff --git a/arrow-cast/src/cast.rs b/arrow-cast/src/cast.rs
index f3dbdb8e06e8..c25f6708ac96 100644
--- a/arrow-cast/src/cast.rs
+++ b/arrow-cast/src/cast.rs
@@ -3285,6 +3285,8 @@ fn cast_to_dictionary<K: ArrowDictionaryKeyType>(
         ),
         Utf8 => pack_string_to_dictionary::<K>(array, cast_options),
         LargeUtf8 => pack_string_to_dictionary::<K>(array, cast_options),
+        Binary => pack_binary_to_dictionary::<K>(array, cast_options),
+        LargeBinary => pack_binary_to_dictionary::<K>(array, cast_options),
         _ => Err(ArrowError::CastError(format!(
             "Unsupported output type for dictionary packing: {:?}",
             dict_value_type
@@ -3348,6 +3350,30 @@ where
     Ok(Arc::new(b.finish()))
 }
 
+// Packs the data as a BinaryDictionaryArray, if possible, with the
+// key types of K
+fn pack_binary_to_dictionary<K>(
+    array: &ArrayRef,
+    cast_options: &CastOptions,
+) -> Result<ArrayRef, ArrowError>
+where
+    K: ArrowDictionaryKeyType,
+{
+    let cast_values = cast_with_options(array, &DataType::Binary, cast_options)?;
+    let values = cast_values.as_any().downcast_ref::<BinaryArray>().unwrap();
+    let mut b = BinaryDictionaryBuilder::<K>::with_capacity(values.len(), 1024, 1024);
+
+    // copy each element one at a time
+    for i in 0..values.len() {
+        if values.is_null(i) {
+            b.append_null();
+        } else {
+            b.append(values.value(i))?;
+        }
+    }
+    Ok(Arc::new(b.finish()))
+}
+
 /// Helper function that takes a primitive array and casts to a (generic) list array.
 fn cast_primitive_to_list<OffsetSize: OffsetSizeTrait + NumCast>(
     array: &ArrayRef,
diff --git a/arrow/tests/array_cast.rs b/arrow/tests/array_cast.rs
index be37a7636b63..91d2da9985b5 100644
--- a/arrow/tests/array_cast.rs
+++ b/arrow/tests/array_cast.rs
@@ -411,7 +411,9 @@ fn get_all_types() -> Vec<DataType> {
         ),
         Dictionary(Box::new(DataType::Int8), Box::new(DataType::Int32)),
         Dictionary(Box::new(DataType::Int16), Box::new(DataType::Utf8)),
+        Dictionary(Box::new(DataType::Int16), Box::new(DataType::Binary)),
         Dictionary(Box::new(DataType::UInt32), Box::new(DataType::Utf8)),
+        Dictionary(Box::new(DataType::UInt32), Box::new(DataType::Binary)),
         Decimal128(38, 0),
         Dictionary(Box::new(DataType::Int8), Box::new(Decimal128(38, 0))),
         Dictionary(Box::new(DataType::Int16), Box::new(Decimal128(38, 0))),