DataOperationsCatalog.TakeRows(IDataView, Int64) Method

Definition

Namespace:

Microsoft.ML

Assembly:

Microsoft.ML.Data.dll

Package:

Microsoft.ML v3.0.1

Take count rows from input.

public Microsoft.ML.IDataView TakeRows (Microsoft.ML.IDataView input, long count);

member this.TakeRows : Microsoft.ML.IDataView * int64 -> Microsoft.ML.IDataView

Public Function TakeRows (input As IDataView, count As Long) As IDataView

Parameters

input

IDataView

The input data.

count

Int64

Number of rows to take.

Returns

IDataView

Examples

using System;
using System.Collections.Generic;
using Microsoft.ML;

namespace Samples.Dynamic
{
    public static class TakeRows
    {
        // Sample class showing how to take some rows from the
        // beginning of IDataView.
        public static void Example()
        {
            // Create a new context for ML.NET operations. It can be used for
            //exception tracking and logging, 
            // as a catalog of available operations and as the source of randomness.
            var mlContext = new MLContext();

            // Get a small dataset as an IEnumerable.
            var enumerableOfData = GetSampleTemperatureData(10);
            var data = mlContext.Data.LoadFromEnumerable(enumerableOfData);

            // Before we apply a filter, examine all the records in the dataset.
            Console.WriteLine($"Date\tTemperature");
            foreach (var row in enumerableOfData)
            {
                Console.WriteLine($"{row.Date.ToString("d")}" +
                    $"\t{row.Temperature}");
            }
            Console.WriteLine();
            // Expected output:
            //  Date    Temperature
            //  1/2/2012        36
            //  1/3/2012        36
            //  1/4/2012        34
            //  1/5/2012        35
            //  1/6/2012        35
            //  1/7/2012        39
            //  1/8/2012        40
            //  1/9/2012        35
            //  1/10/2012       30
            //  1/11/2012       29

            // Take the first 5 rows in the dataset
            var filteredData = mlContext.Data.TakeRows(data, 5);

            // Look at the filtered data and observe that only the first 5 rows are
            // in the resulting dataset.
            var enumerable = mlContext.Data
                .CreateEnumerable<SampleTemperatureData>(filteredData,
                reuseRowObject: true);

            Console.WriteLine($"Date\tTemperature");
            foreach (var row in enumerable)
            {
                Console.WriteLine($"{row.Date.ToString("d")}" +
                    $"\t{row.Temperature}");
            }
            // Expected output:
            //  Date    Temperature
            //  1/2/2012        36
            //  1/3/2012        36
            //  1/4/2012        34
            //  1/5/2012        35
            //  1/6/2012        35
        }

        private class SampleTemperatureData
        {
            public DateTime Date { get; set; }
            public float Temperature { get; set; }
        }

        /// <summary>
        /// Get a fake temperature dataset.
        /// </summary>
        /// <param name="exampleCount">The number of examples to return.</param>
        /// <returns>An enumerable of <see cref="SampleTemperatureData"/>.</returns>
        private static IEnumerable<SampleTemperatureData> GetSampleTemperatureData(
            int exampleCount)

        {
            var rng = new Random(1234321);
            var date = new DateTime(2012, 1, 1);
            float temperature = 39.0f;

            for (int i = 0; i < exampleCount; i++)
            {
                date = date.AddDays(1);
                temperature += rng.Next(-5, 5);
                yield return new SampleTemperatureData
                {
                    Date = date,
                    Temperature =
                    temperature
                };

            }
        }
    }
}

Remarks

Returns returns an IDataView with the first count rows from input.