feat: add mean by dimension and product methods

matrix.d.ts

@@ -2,6 +2,7 @@ declare module 'ml-matrix' {
   type MaybeMatrix = Matrix | number[][];
   type Rng = () => number;
   type ScalarOrMatrix = number | Matrix;
+  type MatrixDimension = 'row' | 'column';
 
   class BaseView extends Matrix {}
   class MatrixColumnView extends BaseView {
@@ -154,13 +155,35 @@ declare module 'ml-matrix' {
      * Returns the sum of all elements of the matrix.
      */
     sum(): number;
+
     /**
-     * Returns the sum by the dimension given.
+     * Returns the sum by the given dimension.
      * @param by - sum by 'row' or 'column'.
      */
-    sum(by: 'row' | 'column'): number[];
+    sum(by: MatrixDimension): number[];
+
+    /**
+     * Returns the product of all elements of the matrix.
+     */
+    product(): number;
+
+    /**
+     * Returns the product by the given dimension.
+     * @param by - product by 'row' or 'column'.
+     */
+    product(by: MatrixDimension): number[];
 
+    /**
+     * Returns the mean of all elements of the matrix.
+     */
     mean(): number;
+
+    /**
+     * Returns the mean by the given dimension.
+     * @param by - mean by 'row' or 'column'.
+     */
+    mean(by: MatrixDimension): number[];
+
     prod(): number;
     norm(type: 'frobenius' | 'max'): number;
     cumulativeSum(): Matrix;

src/__tests__/matrix/mean.js

@@ -0,0 +1,16 @@
+import { Matrix } from '../..';
+
+describe('mean by row and columns', () => {
+  const matrix = new Matrix([[1, 2, 3], [4, 5, 6]]);
+  it('mean by row', () => {
+    expect(matrix.mean('row')).toStrictEqual([2, 5]);
+  });
+
+  it('mean by column', () => {
+    expect(matrix.mean('column')).toStrictEqual([2.5, 3.5, 4.5]);
+  });
+
+  it('mean all', () => {
+    expect(matrix.mean()).toBe(3.5);
+  });
+});

src/__tests__/matrix/product.js

@@ -0,0 +1,16 @@
+import { Matrix } from '../..';
+
+describe('product by row and columns', () => {
+  const matrix = new Matrix([[1, 2, 3], [4, 5, 6]]);
+  it('product by row', () => {
+    expect(matrix.product('row')).toStrictEqual([6, 120]);
+  });
+
+  it('product by column', () => {
+    expect(matrix.product('column')).toStrictEqual([4, 10, 18]);
+  });
+
+  it('product all', () => {
+    expect(matrix.product()).toBe(720);
+  });
+});

src/abstractMatrix.js

@@ -10,7 +10,7 @@ import {
   checkRange,
   checkIndices
 } from './util';
-import { sumByRow, sumByColumn, sumAll } from './stat';
+import { sumByRow, sumByColumn, sumAll, productByRow, productByColumn, productAll } from './stat';
 import MatrixTransposeView from './views/transpose';
 import MatrixRowView from './views/row';
 import MatrixSubView from './views/sub';
@@ -960,12 +960,39 @@ export default function AbstractMatrix(superCtor) {
       }
     }
 
-    /**
-     * Returns the mean of all elements of the matrix
-     * @return {number}
-     */
-    mean() {
-      return this.sum() / this.size;
+    product(by) {
+      switch (by) {
+        case 'row':
+          return productByRow(this);
+        case 'column':
+          return productByColumn(this);
+        case undefined:
+          return productAll(this);
+        default:
+          throw new Error(`invalid option: ${by}`);
+      }
+    }
+
+    mean(by) {
+      const sum = this.sum(by);
+      switch (by) {
+        case 'row': {
+          for (let i = 0; i < this.rows; i++) {
+            sum[i] /= this.columns;
+          }
+          return sum;
+        }
+        case 'column': {
+          for (let i = 0; i < this.columns; i++) {
+            sum[i] /= this.rows;
+          }
+          return sum;
+        }
+        case undefined:
+          return sum / this.size;
+        default:
+          throw new Error(`invalid option: ${by}`);
+      }
     }
 
     /**

src/stat.js

@@ -29,3 +29,33 @@ export function sumAll(matrix) {
   }
   return v;
 }
+
+export function productByRow(matrix) {
+  var sum = newArray(matrix.rows, 1);
+  for (var i = 0; i < matrix.rows; ++i) {
+    for (var j = 0; j < matrix.columns; ++j) {
+      sum[i] *= matrix.get(i, j);
+    }
+  }
+  return sum;
+}
+
+export function productByColumn(matrix) {
+  var sum = newArray(matrix.columns, 1);
+  for (var i = 0; i < matrix.rows; ++i) {
+    for (var j = 0; j < matrix.columns; ++j) {
+      sum[j] *= matrix.get(i, j);
+    }
+  }
+  return sum;
+}
+
+export function productAll(matrix) {
+  var v = 1;
+  for (var i = 0; i < matrix.rows; i++) {
+    for (var j = 0; j < matrix.columns; j++) {
+      v *= matrix.get(i, j);
+    }
+  }
+  return v;
+}

src/util.js

@@ -138,10 +138,10 @@ export function getRange(from, to) {
   return arr;
 }
 
-export function newArray(length) {
+export function newArray(length, value = 0) {
   var array = [];
   for (var i = 0; i < length; i++) {
-    array.push(0);
+    array.push(value);
   }
   return array;
 }