Bug fix: matrix.ToString() when matrix has no rows or columns

Author: jkalias

src/Numerics.Tests/LinearAlgebraTests/Double/DenseMatrixTests.cs

@@ -95,6 +95,38 @@ public void MatrixFrom1DArrayIsReference()
             Assert.AreEqual(10.0, data[0]);
         }
 
+        [Test]
+        public void DescriptionForMatrixWithRowsButNoColumns()
+        {
+            var matrix = TestMatrices["Tall3x2"];
+            matrix = matrix.RemoveColumn(matrix.ColumnCount - 1);
+            matrix = matrix.RemoveColumn(matrix.ColumnCount - 1);
+            Assert.AreEqual("DenseMatrix 3x0-Double\r\n[empty]\r\n[empty]\r\n[empty]\r\n", matrix.ToString());
+        }
+
+        [Test]
+        public void DescriptionForMatrixWithColumnsButNoRows()
+        {
+            var matrix = TestMatrices["Wide2x3"];
+            matrix = matrix.RemoveRow(matrix.RowCount - 1);
+            matrix = matrix.RemoveRow(matrix.RowCount - 1);
+            Assert.AreEqual("DenseMatrix 0x3-Double\r\n[empty]  [empty]  [empty]", matrix.ToString());
+        }
+
+        [Test]
+        public void DescriptionForMatrixWithNoRowsAndNoColumns()
+        {
+            var matrix = TestMatrices["Wide2x3"];
+            matrix = matrix.RemoveRow(matrix.RowCount - 1);
+            matrix = matrix.RemoveRow(matrix.RowCount - 1);
+
+            matrix = matrix.RemoveColumn(matrix.ColumnCount - 1);
+            matrix = matrix.RemoveColumn(matrix.ColumnCount - 1);
+            matrix = matrix.RemoveColumn(matrix.ColumnCount - 1);
+
+            Assert.AreEqual("DenseMatrix 0x0-Double\r\n[empty]", matrix.ToString());
+        }
+
         /// <summary>
         /// Matrix from two-dimensional array is a copy.
         /// </summary>

src/Numerics/LinearAlgebra/Matrix.BCL.cs

@@ -279,7 +279,10 @@ Tuple<int, string[]> FormatColumn(int column, int height, int upper, int lower,
             {
                 c[index++] = formatValue(At(row, column));
             }
-            int w = c.Max(x => x.Length);
+
+            int w = height != 0
+                ? c.Max(x => x.Length)
+                : 0;
             if (withEllipsis)
             {
                 c[upper] = ellipsis;
@@ -289,6 +292,7 @@ Tuple<int, string[]> FormatColumn(int column, int height, int upper, int lower,
 
         static string FormatStringArrayToString(string[,] array, string columnSeparator, string rowSeparator)
         {
+            const string emptyString = "[empty]";
             var rows = array.GetLength(0);
             var cols = array.GetLength(1);
 
@@ -302,35 +306,89 @@ static string FormatStringArrayToString(string[,] array, string columnSeparator,
             }
 
             var sb = new StringBuilder();
-            for (int i = 0; i < rows; i++)
+            if (rows > 0)
             {
-                sb.Append(array[i, 0].PadLeft(widths[0]));
-                for (int j = 1; j < cols; j++)
+                for (int i = 0; i < rows; i++)
                 {
-                    sb.Append(columnSeparator);
-                    sb.Append(array[i, j].PadLeft(widths[j]));
+                    if (cols > 0)
+                    {
+                        sb.Append(array[i, 0].PadLeft(widths[0]));
+                        for (int j = 1; j < cols; j++)
+                        {
+                            sb.Append(columnSeparator);
+                            sb.Append(array[i, j].PadLeft(widths[j]));
+                        }
+                    }
+                    else
+                    {
+                        sb.Append(emptyString);
+                    }
+
+                    sb.Append(rowSeparator);
                 }
-                sb.Append(rowSeparator);
             }
+            else
+            {
+                if (cols > 0)
+                {
+                    for (int j = 0; j < cols; j++)
+                    {
+                        sb.Append(emptyString);
+                        if (j != cols - 1)
+                        {
+                            sb.Append(columnSeparator);
+                        }
+                    }
+                }
+                else
+                {
+                    sb.Append(emptyString);
+                }
+            }
+
             return sb.ToString();
         }
 
         public string ToMatrixString(int upperRows, int lowerRows, int leftColumns, int rightColumns,
             string horizontalEllipsis, string verticalEllipsis, string diagonalEllipsis,
             string columnSeparator, string rowSeparator, Func<T, string> formatValue)
         {
+            var array = ToMatrixStringArray(
+                upperRows,
+                lowerRows,
+                leftColumns,
+                rightColumns,
+                horizontalEllipsis,
+                verticalEllipsis,
+                diagonalEllipsis,
+                formatValue);
+
             return FormatStringArrayToString(
-                ToMatrixStringArray(upperRows, lowerRows, leftColumns, rightColumns, horizontalEllipsis, verticalEllipsis, diagonalEllipsis, formatValue),
-                columnSeparator, rowSeparator);
+                array,
+                columnSeparator,
+                rowSeparator);
         }
 
         public string ToMatrixString(int upperRows, int lowerRows, int minLeftColumns, int rightColumns, int maxWidth,
             string horizontalEllipsis, string verticalEllipsis, string diagonalEllipsis,
             string columnSeparator, string rowSeparator, Func<T, string> formatValue)
         {
+            var array = ToMatrixStringArray(
+                upperRows,
+                lowerRows,
+                minLeftColumns,
+                rightColumns,
+                maxWidth,
+                columnSeparator.Length,
+                horizontalEllipsis,
+                verticalEllipsis,
+                diagonalEllipsis,
+                formatValue);
+
             return FormatStringArrayToString(
-                ToMatrixStringArray(upperRows, lowerRows, minLeftColumns, rightColumns, maxWidth, columnSeparator.Length, horizontalEllipsis, verticalEllipsis, diagonalEllipsis, formatValue),
-                columnSeparator, rowSeparator);
+                array,
+                columnSeparator,
+                rowSeparator);
         }
 
         /// <summary>