numl.Math.LinearAlgebra.Matrix.Col C# (CSharp) Method

        public Vector Col(int i)
        {
            return this[i, VectorType.Col];
        }

        /// <summary>Gets best split.</summary>
        /// <param name="x">The Matrix to process.</param>
        /// <param name="y">The Vector to process.</param>
        /// <param name="used">The used.</param>
        /// <returns>The best split.</returns>
        private Tuple<int, double, Impurity> GetBestSplit(Matrix x, Vector y, List<int> used)
        {
            double bestGain = -1;
            int bestFeature = -1;

            Impurity bestMeasure = null;
            for (int i = 0; i < x.Cols; i++)
            {
                // already used?
                if (used.Contains(i)) continue;

                double gain = 0;

                Impurity measure = (Impurity)Ject.Create(ImpurityType);

                // get appropriate column vector
                var feature = x.Col(i);
                // get appropriate feature at index i
                // (important on because of multivalued
                // cols)
                var property = Descriptor.At(i);
                // if discrete, calculate full relative gain
                if (property.Discrete)
                    gain = measure.RelativeGain(y, feature);
                // otherwise segment based on width
                else
                    gain = measure.SegmentedRelativeGain(y, feature, Width);

                // best one?
                if (gain > bestGain)
                {
                    bestGain = gain;
                    bestFeature = i;
                    bestMeasure = measure;
                }
            }

            return new Tuple<int, double, Impurity>(bestFeature, bestGain, bestMeasure);
        }