feat: implement reverseRows and reverseColumns methods

Author: targos

matrix.d.ts

@@ -186,19 +186,21 @@ declare module 'ml-matrix' {
 
     prod(): number;
     norm(type: 'frobenius' | 'max'): number;
-    cumulativeSum(): Matrix;
+    cumulativeSum(): this;
     dot(vector2: Matrix): number;
     mmul(other: Matrix): Matrix;
     strassen2x2(other: Matrix): Matrix;
     strassen3x3(other: Matrix): Matrix;
     mmulStrassen(y: Matrix): Matrix;
     scaleRows(min?: number, max?: number): Matrix;
     scaleColumns(min?: number, max?: number): Matrix;
+    reverseRows(): this;
+    reverseColumns(): this;
     kroneckerProduct(other: Matrix): Matrix;
     tensorProduct(other: Matrix): Matrix;
     transpose(): Matrix;
-    sortRows(compareFunction: Function): Matrix;
-    sortColumns(compareFunction: Function): Matrix;
+    sortRows(compareFunction: Function): this;
+    sortColumns(compareFunction: Function): this;
     subMatrix(
       startRow: number,
       endRow: number,

src/__tests__/matrix/reverse.js

@@ -0,0 +1,17 @@
+import { Matrix } from '../..';
+
+describe('revers rows and columns', () => {
+  it('reverse rows', () => {
+    const matrix = new Matrix([[1, 2, 3], [4, 5, 6]]);
+    const result = matrix.reverseRows();
+    expect(result).toBe(matrix);
+    expect(result.to2DArray()).toStrictEqual([[3, 2, 1], [6, 5, 4]]);
+  });
+
+  it('reverse columns', () => {
+    const matrix = new Matrix([[1, 2, 3], [4, 5, 6]]);
+    const result = matrix.reverseColumns();
+    expect(result).toBe(matrix);
+    expect(result.to2DArray()).toStrictEqual([[4, 5, 6], [1, 2, 3]]);
+  });
+});

src/abstractMatrix.js

@@ -1383,6 +1383,32 @@ export default function AbstractMatrix(superCtor) {
       return newMatrix;
     }
 
+    reverseRows() {
+      const middle = Math.ceil(this.columns / 2);
+      for (var i = 0; i < this.rows; i++) {
+        for (var j = 0; j < middle; j++) {
+          var first = this.get(i, j);
+          var last = this.get(i, this.columns - 1 - j);
+          this.set(i, j, last);
+          this.set(i, this.columns - 1 - j, first);
+        }
+      }
+      return this;
+    }
+
+    reverseColumns() {
+      const middle = Math.ceil(this.rows / 2);
+      for (var j = 0; j < this.columns; j++) {
+        for (var i = 0; i < middle; i++) {
+          var first = this.get(i, j);
+          var last = this.get(this.rows - 1 - i, j);
+          this.set(i, j, last);
+          this.set(this.rows - 1 - i, j, first);
+        }
+      }
+      return this;
+    }
+
     /**
      * Returns the Kronecker product (also known as tensor product) between this and other
      * See https://en.wikipedia.org/wiki/Kronecker_product