source: branches/3106_AnalyticContinuedFractionsRegression/HeuristicLab.Problems.DataAnalysis/3.4/DatasetExtensions.cs

#region License Information
/* HeuristicLab
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 *
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 * it under the terms of the GNU General Public License as published by
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
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#endregion

using System;
using System.Collections.Generic;
using System.Linq;

namespace HeuristicLab.Problems.DataAnalysis {
  public static class DatasetExtensions {
    public static double[,] ToArray(this IDataset dataset, IEnumerable<string> variables, IEnumerable<int> rows) {
      return ToArray(dataset,
        variables,
        transformations: variables.Select(_ => (ITransformation<double>)null), // no transform
        rows: rows);
    }
    public static double[,] ToArray(this IDataset dataset, IEnumerable<string> variables,
      IEnumerable<ITransformation<double>> transformations, IEnumerable<int> rows) {
      string[] variablesArr = variables.ToArray();
      int[] rowsArr = rows.ToArray();
      ITransformation<double>[] transformArr = transformations.ToArray();
      if (transformArr.Length != variablesArr.Length)
        throw new ArgumentException("Number of variables and number of transformations must match.");

      double[,] matrix = new double[rowsArr.Length, variablesArr.Length];

      for (int i = 0; i < variablesArr.Length; i++) {
        var origValues = dataset.GetDoubleValues(variablesArr[i], rowsArr);
        var values = transformArr[i] != null ? transformArr[i].Apply(origValues) : origValues;
        int row = 0;
        foreach (var value in values) {
          matrix[row, i] = value;
          row++;
        }
      }

      return matrix;
    }

    /// <summary>
    /// Prepares a binary data matrix from a number of factors and specified factor values
    /// </summary>
    /// <param name="dataset">A dataset that contains the variable values</param>
    /// <param name="factorVariables">An enumerable of categorical variables (factors). For each variable an enumerable of values must be specified.</param>
    /// <param name="rows">An enumerable of row indices for the dataset</param>
    /// <returns></returns>
    /// <remarks>Factor variables (categorical variables) are split up into multiple binary variables one for each specified value.</remarks>
    public static double[,] ToArray(
      this IDataset dataset,
      IEnumerable<KeyValuePair<string, IEnumerable<string>>> factorVariables,
      IEnumerable<int> rows) {
      // check input variables. Only string variables are allowed.
      var invalidInputs =
        factorVariables.Select(kvp => kvp.Key).Where(name => !dataset.VariableHasType<string>(name));
      if (invalidInputs.Any())
        throw new NotSupportedException("Unsupported inputs: " + string.Join(", ", invalidInputs));

      int numBinaryColumns = factorVariables.Sum(kvp => kvp.Value.Count());

      List<int> rowsList = rows.ToList();
      double[,] matrix = new double[rowsList.Count, numBinaryColumns];

      int col = 0;
      foreach (var kvp in factorVariables) {
        var varName = kvp.Key;
        var cats = kvp.Value;
        if (!cats.Any()) continue;
        foreach (var cat in cats) {
          var values = dataset.GetStringValues(varName, rows);
          int row = 0;
          foreach (var value in values) {
            matrix[row, col] = value == cat ? 1 : 0;
            row++;
          }
          col++;
        }
      }
      return matrix;
    }

    public static IntervalCollection GetIntervals(this IDataset dataset) {
      IntervalCollection intervalCollection = new IntervalCollection();
      foreach (var variable in dataset.DoubleVariables) { // intervals are only possible for double variables
        var variableInterval = Interval.GetInterval(dataset.GetDoubleValues(variable));
        intervalCollection.AddInterval(variable, variableInterval);
      }

      return intervalCollection;
    }

    public static IEnumerable<KeyValuePair<string, IEnumerable<string>>> GetFactorVariableValues(
      this IDataset ds, IEnumerable<string> factorVariables, IEnumerable<int> rows) {
      return from factor in factorVariables
             let distinctValues = ds.GetStringValues(factor, rows).Distinct().ToArray()
             // 1 distinct value => skip (constant)
             // 2 distinct values => only take one of the two values
             // >=3 distinct values => create a binary value for each value
             let reducedValues = distinctValues.Length <= 2
               ? distinctValues.Take(distinctValues.Length - 1)
               : distinctValues
             select new KeyValuePair<string, IEnumerable<string>>(factor, reducedValues);
    }
  }
}