CurtHagenlocher commented on code in PR #260: URL: https://github.com/apache/arrow-dotnet/pull/260#discussion_r3042674515
########## src/Apache.Arrow/Arrays/RunEndEncodedArray.cs: ########## @@ -0,0 +1,222 @@ +// 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; +using Apache.Arrow.Types; + +namespace Apache.Arrow; + +/// <summary> +/// Represents a run-end encoded array. +/// A run-end encoded array stores consecutive runs of the same value more efficiently. +/// It contains two child arrays: run_ends (Int16/Int32/Int64) and values (any type). +/// The run_ends array stores the cumulative end positions of each run. +/// </summary> +public class RunEndEncodedArray : Array +{ + /// <summary> + /// Gets the run ends array (Int16Array, Int32Array, or Int64Array). + /// This array contains the cumulative end indices for each run. + /// </summary> + public IArrowArray RunEnds { get; } + + /// <summary> + /// Gets the values array. + /// This array contains the actual values that are run-length encoded. + /// </summary> + public IArrowArray Values { get; } + + /// <summary> + /// Creates a new RunEndEncodedArray from ArrayData. + /// </summary> + /// <param name="data">The array data containing run ends and values as children.</param> + public RunEndEncodedArray(ArrayData data) + : this(data, ArrowArrayFactory.BuildArray(data.Children[0]), ArrowArrayFactory.BuildArray(data.Children[1])) + { + } + + /// <summary> + /// Creates a new RunEndEncodedArray with specified run ends and values arrays. + /// </summary> + /// <param name="runEnds">The run ends array (must be Int16Array, Int32Array, or Int64Array).</param> + /// <param name="values">The values array (can be any type).</param> + public RunEndEncodedArray(IArrowArray runEnds, IArrowArray values) + : this(CreateArrayData(runEnds, values), runEnds, values) + { + } + + private RunEndEncodedArray(ArrayData data, IArrowArray runEnds, IArrowArray values) + : base(data) + { + data.EnsureBufferCount(0); // REE arrays have no buffers, only children + data.EnsureDataType(ArrowTypeId.RunEndEncoded); + + ValidateRunEndsType(runEnds); + RunEnds = runEnds; + Values = values; + } + + private static ArrayData CreateArrayData(IArrowArray runEnds, IArrowArray values) + { + ValidateRunEndsType(runEnds); + + // The logical length of a REE array is determined by the last value in run_ends + int logicalLength = GetLogicalLength(runEnds); + + var dataType = new RunEndEncodedType(runEnds.Data.DataType, values.Data.DataType); + + return new ArrayData( + dataType, + logicalLength, + nullCount: 0, // REE arrays don't have a validity bitmap + offset: 0, + buffers: [], + children: [runEnds.Data, values.Data]); + } + + private static void ValidateRunEndsType(IArrowArray runEnds) + { + ArrowTypeId typeId = runEnds.Data.DataType.TypeId; + if (typeId != ArrowTypeId.Int16 && + typeId != ArrowTypeId.Int32 && + typeId != ArrowTypeId.Int64) + { + throw new ArgumentException( + $"Run ends array must be Int16, Int32, or Int64, but got {typeId}", + nameof(runEnds)); + } + } + + private static int GetLogicalLength(IArrowArray runEnds) + { + if (runEnds.Length == 0) + { + return 0; + } + + // Get the last run end value which represents the logical length + switch (runEnds) + { + case Int16Array int16Array: + return int16Array.GetValue(int16Array.Length - 1) ?? 0; + case Int32Array int32Array: + return int32Array.GetValue(int32Array.Length - 1) ?? 0; + case Int64Array int64Array: + { + long? lastValue = int64Array.GetValue(int64Array.Length - 1); + if (lastValue.HasValue && lastValue.Value > int.MaxValue) + { + throw new ArgumentException("Run ends value exceeds maximum supported length."); Review Comment: There's not much advantage in returning a long here that would immediately have to be passed to an `ArrayData` constructor that only takes an int. :( -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
