Implement count based on size (#2092)

* Implement count based on size

Closes #2085

* Improve count implementation

Co-authored-by: Jos de Jong <wjosdejong@gmail.com>

src/factoriesAny.js

@@ -64,6 +64,7 @@ export { createOr } from './function/logical/or.js'
 export { createXor } from './function/logical/xor.js'
 export { createConcat } from './function/matrix/concat.js'
 export { createColumn } from './function/matrix/column.js'
+export { createCount } from './function/matrix/count.js'
 export { createCross } from './function/matrix/cross.js'
 export { createDiag } from './function/matrix/diag.js'
 export { createFilter } from './function/matrix/filter.js'

src/function/matrix/count.js

@@ -0,0 +1,37 @@
+import { factory } from '../../utils/factory.js'
+
+const name = 'count'
+const dependencies = ['typed', 'size', 'prod']
+
+export const createCount = /* #__PURE__ */ factory(name, dependencies, ({ typed, size, prod }) => {
+  /**
+   * Count the number of elements of a matrix, array or string.
+   *
+   * Syntax:
+   *
+   *     math.count(x)
+   *
+   * Examples:
+   *
+   *     math.count('hello world')        // returns 11
+   *     const A = [[1, 2, 3], [4, 5, 6]]
+   *     math.count(A)                    // returns 6
+   *     math.count(math.range(1,6))      // returns 5
+   *
+   * See also:
+   *
+   *     size
+   *
+   * @param {string | Array | Matrix} x  A matrix or string
+   * @return {number} An integer with the elements in `x`.
+   */
+  return typed(name, {
+    string: function (x) {
+      return x.length
+    },
+
+    'Matrix | Array': function (x) {
+      return prod(size(x))
+    }
+  })
+})

src/function/matrix/size.js

@@ -24,7 +24,7 @@ export const createSize = /* #__PURE__ */ factory(name, dependencies, ({ typed,
    *
    * See also:
    *
-   *     resize, squeeze, subset
+   *     count, resize, squeeze, subset
    *
    * @param {boolean | number | Complex | Unit | string | Array | Matrix} x  A matrix
    * @return {Array | Matrix} A vector with size of `x`.

test/unit-tests/function/matrix/count.test.js

@@ -0,0 +1,40 @@
+import assert from 'assert'
+import math from '../../../../src/defaultInstance.js'
+
+const { count, matrix, sparse } = math
+
+describe('count', function () {
+  it('should count arrays', function () {
+    assert.strictEqual(count([[1, 2, 3], [4, 5, 6]]), 6)
+    assert.strictEqual(count([[[1, 2], [3, 4]], [[5, 6], [7, 8]]]), 8)
+    assert.strictEqual(count([]), 0)
+    assert.strictEqual(count([[]]), 0)
+  })
+
+  it('should count dense matrices', function () {
+    assert.strictEqual(count(matrix([[1, 2, 3], [4, 5, 6]])), 6)
+    assert.strictEqual(count(matrix([[[1, 2], [3, 4]], [[5, 6], [7, 8]]])), 8)
+    assert.strictEqual(count(matrix([])), 0)
+    assert.strictEqual(count(matrix([[]])), 0)
+  })
+
+  it('should count sparse matrices', function () {
+    assert.strictEqual(count(sparse([[1, 2, 3], [4, 5, 6]])), 6)
+    assert.strictEqual(count(sparse([])), 0)
+    assert.strictEqual(count(sparse([[]])), 0)
+  })
+
+  it('should count strings', function () {
+    assert.strictEqual(count('123456'), 6)
+    assert.strictEqual(count(''), 0)
+  })
+
+  it('should throw an error if called with an invalid number of arguments', function () {
+    assert.throws(function () { count() }, /TypeError: Too few arguments/)
+    assert.throws(function () { count(1, 2) }, /TypeError: Too many arguments/)
+  })
+
+  it('should throw an error if called with invalid type of arguments', function () {
+    assert.throws(function () { count(new Date()) }, /TypeError: Unexpected type of argument/)
+  })
+})