Example of creating a StructArray

Example.cs

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//     http://www.apache.org/licenses/LICENSE-2.0
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using Apache.Arrow.Ipc;
using Apache.Arrow.Types;
using System.Collections.Generic;
using System.IO;
using Xunit;

namespace Apache.Arrow.Tests
{
    public class StructArrayTests
    {
        public class Point
        {
            public double X { get; set; }
            public double Y { get; set; }
        }

        public class ScoredPoint
        {
            public Point Location { get; set; }
            public int Score { get; set; }
        }

        [Fact]
        public void Example()
        {
            Field.Builder fieldBuilder = new Field.Builder();

            List<Field> pointFields = new List<Field>();
            pointFields.Add(fieldBuilder.Name("x").DataType(DoubleType.Default).Nullable(true).Build());
            pointFields.Add(fieldBuilder.Name("y").DataType(DoubleType.Default).Nullable(true).Build());
            StructType pointType = new StructType(pointFields);

            List<Field> scoredPointFields = new List<Field>();
            scoredPointFields.Add(fieldBuilder.Name("location").DataType(pointType).Nullable(true).Build());
            scoredPointFields.Add(fieldBuilder.Name("score").DataType(Int32Type.Default).Nullable(true).Build());
            StructType scoredPointType = new StructType(scoredPointFields);

            List<ScoredPoint> inputData = new List<ScoredPoint> {
                new ScoredPoint {
                    Location = new Point { X = 0, Y = 0 }, Score = 100
                },
                new ScoredPoint {
                    Location = new Point { X = 10, Y = 5 }, Score = 10
                }
            };

            int numRows = inputData.Count;
            // Skipping nulls for this example
            int numNulls = 0;
            // Normally you woudln't need to manually set the offset because you'd be using a 
            // StructArray.Builder but it seems a StructArray.Builder doesn't exist so we will
            // create the array directly.  We can always use 0 for offset (this gets set when
            // an array is created by slicing)
            int offset = 0;

            // In a struct array, each field is its own array.
            DoubleArray.Builder xBuilder = new DoubleArray.Builder();
            DoubleArray.Builder yBuilder = new DoubleArray.Builder();
            Int32Array.Builder scoreBuilder = new Int32Array.Builder();
            // I can't figure out how to specify null for the validity bitmap so we will just
            // create one that is "all-valid" since we don't have any nulls for this example.
            ArrowBuffer.BitmapBuilder nullBitmap = new ArrowBuffer.BitmapBuilder();

            // Converting from row-major to column-major
            foreach (var scoredPoint in inputData)
            {
                xBuilder.Append(scoredPoint.Location.X);
                yBuilder.Append(scoredPoint.Location.Y);
                scoreBuilder.Append(scoredPoint.Score);
                nullBitmap.Append(true);
            }

            ArrowBuffer nullBuffer = nullBitmap.Build();

            // Order matters here, it needs to match the order specified when we created the type (e.g. pointType)
            List<Array> pointArrays = new List<Array> { xBuilder.Build(), yBuilder.Build() };
            StructArray points = new StructArray(pointType, numRows, pointArrays, nullBuffer, numNulls, offset);
            List<Array> scoredPointArrays = new List<Array> { points, scoreBuilder.Build() };
            // We can reuse the null buffer
            StructArray scoredPoints = new StructArray(scoredPointType, numRows, scoredPointArrays, nullBuffer, numNulls, offset);
        }
    }
}