feat: #155 math related functions

src/math/mean.ts

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+import { sum } from './sum';
+
+
+/**
+ *
+ * Mean (avg) values
+ * @since 5.18.0
+ * @category Math
+ * @param values
+ *
+ */
+export function mean(values: Float64Array) {
+  return sum(values) / values.length;
+}
+
+export default mean;

src/math/stdDeviation.ts

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+import variance from './variance';
+
+
+/**
+ * Standard Deviation
+ * @since 5.18.0
+ * @category Math
+ * @param values
+ */
+export function stdDeviation(values: Float64Array): number {
+  return Math.sqrt(variance(values));
+}

src/math/sum.ts

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+
+
+/**
+ * Math sum
+ * @category Math
+ * @since 5.18.0
+ * @param values
+ */
+export function sum(values: Float64Array): number {
+  return values.reduce((pre, value) => pre + value, 0);
+}
+
+export default sum;

src/math/util.ts

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+import forEach from '../forEach';
+
+
+/**
+ * check array all are numbers
+ *
+ * @private
+ * @internal
+ * @ignore
+ * @since 5.18.0
+ * @param values
+ */
+export function checkArray(values: ArrayLike<any>) {
+  forEach(values, (value, idx) => {
+    const tValue = typeof value;
+    if (tValue !== 'number' && tValue !== 'bigint') {
+      throw new TypeError(`array[${idx}] is ${tValue}, all items must be number`);
+    }
+    if (value === NaN) {
+      throw new TypeError(`array[${idx}] is NaN, all items must be number`);
+    }
+  });
+}

src/math/variance.ts

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+import mean from './mean';
+import sum from './sum';
+
+/**
+ * Variance
+ * @since 5.18.0
+ * @category Math
+ *
+ * @param values
+ */
+export function variance(values: Float64Array): number {
+  const mValue = mean(values);
+  return sum(values.map((value) => (value - mValue) ** 2)) / values.length;
+}
+
+export default variance;

test/math.test.ts

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+import { mean } from '../src/math/mean';
+import { stdDeviation } from '../src/math/stdDeviation';
+import { sum } from '../src/math/sum';
+import { variance } from '../src/math/variance';
+
+
+describe('math', () => {
+
+  it('should support sum', () => {
+
+    expect(sum(Float64Array.from([1, 23, 4]))).toBe(28);
+    expect(sum(Float64Array.from([1.2, 3.1, 0.3]))).toBe(4.6);
+
+  });
+
+  it('should support mean', () => {
+
+    expect(mean(Float64Array.from([1, 7, 4]))).toBe(4);
+    expect(mean(Float64Array.from([1.2, 3, 0.3]))).toBe(1.5);
+
+  });
+
+  it('should support variance', () => {
+
+    expect(variance(Float64Array.from([600, 470, 170, 430, 300]))).toBe(21704);
+
+  });
+
+  it('should support standard deviation', () => {
+
+    expect(stdDeviation(Float64Array.from([600, 470, 170, 430, 300]))).toBe(147.32277488562318);
+
+  });
+
+
+});