Add an algorithm to find mean absolute deviation (#1165)

Maths/MeanAbsoluteDeviation.js

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+import { mean } from './AverageMean.js'
+/**
+ *@function meanAbsoluteDeviation
+ *@description Calculates the mean absolute deviation of list of numbers
+ * @param {Integer} data
+ * @returns meanAbsoluteDeviation([2,34,5,0,-2]) = 10.480
+ * @url https://en.wikipedia.org/wiki/Average_absolute_deviation
+ */
+function meanAbsoluteDeviation (data) {
+  if (!Array.isArray(data)) {
+    throw new TypeError('Invalid Input')
+  }
+  let absoluteSum = 0
+  const meanValue = mean(data)
+  for (const dataPoint of data) {
+    absoluteSum += Math.abs(dataPoint - meanValue)
+  }
+  return absoluteSum / data.length
+}
+
+export {
+  meanAbsoluteDeviation
+}

Maths/test/MeanAbsoluteDeviation.test.js

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+import { meanAbsoluteDeviation } from '../MeanAbsoluteDeviation.js'
+
+describe('tests for mean absolute deviation', () => {
+  it('should be a function', () => {
+    expect(typeof meanAbsoluteDeviation).toEqual('function')
+  })
+
+  it('should throw an invalid input error', () => {
+    expect(() => meanAbsoluteDeviation('fgh')).toThrow()
+  })
+
+  it('should return the mean absolute devition of an array of numbers', () => {
+    const meanAbDev = meanAbsoluteDeviation([2, 34, 5, 0, -2])
+    expect(meanAbDev).toBe(10.479999999999999)
+  })
+})