DataOperationsCatalog.FilterRowsByColumn Metodo

Definizione

Spazio dei nomi:

Microsoft.ML

Assembly:

Microsoft.ML.Data.dll

Pacchetto:

Microsoft.ML v2.0.0

Filtrare il set di dati in base ai valori di una colonna numerica.

public Microsoft.ML.IDataView FilterRowsByColumn (Microsoft.ML.IDataView input, string columnName, double lowerBound = -∞, double upperBound = ∞);

member this.FilterRowsByColumn : Microsoft.ML.IDataView * string * double * double -> Microsoft.ML.IDataView

Public Function FilterRowsByColumn (input As IDataView, columnName As String, Optional lowerBound As Double = -∞, Optional upperBound As Double = ∞) As IDataView

Parametri

input

IDataView

Dati di input.

columnName

String

Nome di una colonna da usare per il filtro.

lowerBound

Double

Limite inferiore inclusivo.

upperBound

Double

Limite superiore esclusivo.

Restituisce

IDataView

Esempio

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

namespace Samples.Dynamic
{
    public static class FilterRowsByColumn
    {
        // // Sample class showing how to filter out some rows in
        // 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

            // Filter the data by the values of the temperature. The lower bound is
            // inclusive, the upper exclusive.
            var filteredData = mlContext.Data
                .FilterRowsByColumn(data, columnName: "Temperature",
                lowerBound: 34, upperBound: 37);

            // Look at the filtered data and observe that values outside [34,37)
            // have been dropped.
            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
            //  1/9/2012        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
                };

            }
        }
    }
}

Commenti

Mantenere solo le righe che soddisfano la condizione di intervallo: il valore della colonna columnName deve essere compreso tra lowerBound (inclusivo) e upperBound (esclusivo).