Add Parquet variant shredding support

src/Apache.Arrow.Operations/Apache.Arrow.Operations.csproj

@@ -18,6 +18,7 @@
   </ItemGroup>
 
   <ItemGroup>
+    <ProjectReference Include="..\Apache.Arrow\Apache.Arrow.csproj" />
     <ProjectReference Include="..\Apache.Arrow.Scalars\Apache.Arrow.Scalars.csproj" />
   </ItemGroup>
 

src/Apache.Arrow.Operations/Shredding/ShredOptions.cs

@@ -0,0 +1,50 @@
+// Licensed to the Apache Software Foundation (ASF) under one or more
+// contributor license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright ownership.
+// The ASF licenses this file to You under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance with
+// the License.  You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+namespace Apache.Arrow.Operations.Shredding
+{
+    /// <summary>
+    /// Options controlling how <see cref="ShredSchemaInferer"/> infers a shredding schema.
+    /// </summary>
+    public sealed class ShredOptions
+    {
+        /// <summary>
+        /// Maximum nesting depth for shredded objects and arrays.
+        /// 0 means only top-level fields are shredded.
+        /// Default is 3.
+        /// </summary>
+        public int MaxDepth { get; set; } = 3;
+
+        /// <summary>
+        /// Minimum fraction of values (0.0–1.0) in which a field must appear
+        /// to be considered for shredding. Fields appearing less frequently
+        /// than this threshold are left in the binary residual.
+        /// Default is 0.5 (50%).
+        /// </summary>
+        public double MinFieldFrequency { get; set; } = 0.5;
+
+        /// <summary>
+        /// Minimum fraction of non-null values (0.0–1.0) for a field that must
+        /// share the same type for the field to be shredded as a typed column.
+        /// If the type consistency is below this threshold, the field gets a
+        /// <see cref="ShredType.None"/> schema (binary-only).
+        /// Default is 0.8 (80%).
+        /// </summary>
+        public double MinTypeConsistency { get; set; } = 0.8;
+
+        /// <summary>Default options.</summary>
+        public static ShredOptions Default => new ShredOptions();
+    }
+}

src/Apache.Arrow.Operations/Shredding/ShredResult.cs

@@ -0,0 +1,109 @@
+// Licensed to the Apache Software Foundation (ASF) under one or more
+// contributor license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright ownership.
+// The ASF licenses this file to You under the Apache License, Version 2.0
+// (the "License"); you may not use this file except in compliance with
+// the License.  You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+using System.Collections.Generic;
+
+namespace Apache.Arrow.Operations.Shredding
+{
+    /// <summary>
+    /// The result of shredding a single variant value: a (value, typed_value) pair.
+    /// <para>
+    /// Follows the Parquet variant shredding spec encoding matrix:
+    /// <list type="bullet">
+    /// <item>Both null → missing (only valid for object sub-fields)</item>
+    /// <item>value non-null, typed_value null → unshredded (value in binary)</item>
+    /// <item>value null, typed_value non-null → fully shredded into typed column</item>
+    /// <item>Both non-null → partially shredded object (typed_value has shredded fields, value has residual)</item>
+    /// </list>
+    /// </para>
+    /// </summary>
+    public sealed class ShredResult
+    {
+        /// <summary>
+        /// The residual variant value bytes. These reference the column-level metadata
+        /// returned by <see cref="VariantShredder.Shred(IEnumerable{Scalars.Variant.VariantValue}, ShredSchema)"/>;
+        /// they are NOT self-contained. Non-null when the value (or part of it) could
+        /// not be shredded into the typed column. For partially shredded objects this
+        /// contains only the unshredded fields.
+        /// </summary>
+        public byte[] Value { get; }
+
+        /// <summary>
+        /// The typed value extracted according to the schema. The runtime type depends
+        /// on the <see cref="ShredSchema.TypedValueType"/>:
+        /// <list type="bullet">
+        /// <item>Primitives: the corresponding CLR type (bool, int, long, double, string, etc.)</item>
+        /// <item>Object: <see cref="ShredObjectResult"/></item>
+        /// <item>Array: <see cref="ShredArrayResult"/></item>
+        /// </list>
+        /// Null when the value does not match the schema type (falls back to binary).
+        /// </summary>
+        public object TypedValue { get; }
+
+        /// <summary>
+        /// True when both <see cref="Value"/> and <see cref="TypedValue"/> are null,
+        /// indicating the field is missing (only valid for object sub-fields).
+        /// </summary>
+        public bool IsMissing => Value == null && TypedValue == null;
+
+        /// <summary>Creates a shred result.</summary>
+        public ShredResult(byte[] value, object typedValue)
+        {
+            Value = value;
+            TypedValue = typedValue;
+        }
+
+        /// <summary>A missing result (both null).</summary>
+        public static readonly ShredResult Missing = new ShredResult(null, null);
+    }
+
+    /// <summary>
+    /// The typed_value result for a shredded object. Contains one <see cref="ShredResult"/>
+    /// per field defined in the object's <see cref="ShredSchema"/>.
+    /// </summary>
+    public sealed class ShredObjectResult
+    {
+        /// <summary>
+        /// Shredded fields, keyed by field name matching the <see cref="ShredSchema.ObjectFields"/>.
+        /// Each entry is the shredded (value, typed_value) pair for that field.
+        /// </summary>
+        public IReadOnlyDictionary<string, ShredResult> Fields { get; }
+
+        /// <summary>Creates a shredded object result.</summary>
+        public ShredObjectResult(IReadOnlyDictionary<string, ShredResult> fields)
+        {
+            Fields = fields;
+        }
+    }
+
+    /// <summary>
+    /// The typed_value result for a shredded array. Contains one <see cref="ShredResult"/>
+    /// per element in the source array.
+    /// </summary>
+    public sealed class ShredArrayResult
+    {
+        /// <summary>
+        /// Shredded elements. Each entry is the shredded (value, typed_value) pair for that element.
+        /// Array elements are never missing — null elements are encoded as variant null in the value column.
+        /// </summary>
+        public IReadOnlyList<ShredResult> Elements { get; }
+
+        /// <summary>Creates a shredded array result.</summary>
+        public ShredArrayResult(IReadOnlyList<ShredResult> elements)
+        {
+            Elements = elements;
+        }
+    }
+}