/// <summary>
/// Gets the transpose of a matrix.
/// </summary>
///
/// <param name="matrix">A matrix.</param>
///
/// <returns>The transpose of the given matrix.</returns>
///
public static TItem[][] Transpose <TCollection, TItem>(this TCollection matrix)
where TCollection : ICollection, IEnumerable <TItem[]>
{
int rows = matrix.Count;
if (rows == 0)
{
return(new TItem[rows][]);
}
int cols = matrix.Columns();
#if CHECKS
if (!IsRectangular(matrix))
{
throw new ArgumentException("Only rectangular matrices can be transposed.");
}
#endif
TItem[][] result = Jagged.Zeros <TItem>(cols, rows);
int i = 0;
foreach (TItem[] row in matrix)
{
for (int j = 0; j < result.Length; j++)
{
result[j][i] = row[j];
}
i++;
}
return(result);
}
/// <summary>
/// Removes dimensions of length 1 from the array.
/// </summary>
///
/// <param name="array">The array.</param>
///
public static Array Squeeze(this Array array)
{
int[] dimensions = array.GetLength().Where(x => x != 1).ToArray();
if (dimensions.Length == 0)
{
dimensions = new[] { 1 }
}
;
Array res;
if (array.IsJagged())
{
#if NETSTANDARD1_4
throw new NotSupportedException("Squeeze with jagged arrays is not supported in .NET Standard 1.4.");
#else
res = Jagged.Zeros(array.GetInnerMostType(), dimensions);
Copy(array, res);
#endif
}
else
{
res = Matrix.Zeros(array.GetInnerMostType(), dimensions);
Buffer.BlockCopy(array, 0, res, 0, res.GetNumberOfBytes());
}
return(res);
}
/// <summary>
/// Calculates the scatter matrix of a sample matrix.
/// </summary>
///
/// <remarks>
/// By dividing the Scatter matrix by the sample size, we get the population
/// Covariance matrix. By dividing by the sample size minus one, we get the
/// sample Covariance matrix.
/// </remarks>
///
/// <param name="matrix">A number multi-dimensional array containing the matrix values.</param>
/// <param name="means">The mean value of the given values, if already known.</param>
/// <param name="divisor">A real number to divide each member of the matrix.</param>
/// <param name="dimension">
/// Pass 0 if the mean vector is a row vector, 1 otherwise. Default value is 0.
/// </param>
///
/// <returns>The covariance matrix.</returns>
///
public static float[][] Scatter(this float[][] matrix, int dimension, float[] means)
{
int rows = matrix.Rows();
int cols = matrix.Columns();
float[][] cov;
if (dimension == 0)
{
if (means.Length != cols)
throw new ArgumentException("Length of the mean vector should equal the number of columns", "means");
cov = Jagged.Zeros<float>(cols, cols);
for (int i = 0; i < cols; i++)
{
for (int j = i; j < cols; j++)
{
float s = 0;
for (int k = 0; k < rows; k++)
{
var v = matrix[k][j] - means[j];
s += v * v;
}
cov[i][j] = s;
cov[j][i] = s;
}
}
}
else if (dimension == 1)
{
if (means.Length != rows)
throw new ArgumentException("Length of the mean vector should equal the number of rows", "means");
cov = Jagged.Zeros<float>(rows, rows);
for (int i = 0; i < rows; i++)
{
for (int j = i; j < rows; j++)
{
float s = 0;
for (int k = 0; k < cols; k++)
{
var v = matrix[j][k] - means[j];
s += v * v;
}
cov[i][j] = s;
cov[j][i] = s;
}
}
}
else
{
throw new ArgumentException("Invalid dimension.", "dimension");
}
return cov;
}
/// <summary>
/// Converts a matrix represented as a nested list of lists into a jagged matrix.
/// </summary>
///
public static T[][] ToJagged <T>(this IList <IList <T> > values)
{
int rows = values.Rows();
int cols = values.Columns();
T[][] result = Jagged.Zeros <T>(rows, cols);
for (int i = 0; i < values.Count; i++)
{
for (int j = 0; j < values[i].Count; j++)
{
result[i][j] = values[i][j];
}
}
return(result);
}
