feat(median): Add median function (#141)

* feat(median): Add median function

Add a function to find the median value of a numeric array.

* test(median): Add tests for median

Author: mihhu

src/array-median.js

@@ -0,0 +1,32 @@
+export default median
+
+/**
+ * Original source: https://stackoverflow.com/a/29544442/4573129
+ * This method will return the median value of an array
+ * @param {Array} array - the array to find the median
+ * @return {Number} - the median of the values in the array
+ */
+
+function median(array) {
+  if (!Array.isArray(array)) {
+    return `${array} is not an array.`
+  }
+  if (array.some(isNaN)) {
+    return `${array} contains non-numeric items.`
+  }
+  if (array.length === 0) {
+    return `${array} has no items.`
+  }
+
+  let medianValue = 0
+  const sortedArray = array.sort((curr, next) => (curr - next))
+  const index = Math.floor(sortedArray.length / 2)
+
+  if (sortedArray.length % 2 === 0) {
+    medianValue = (sortedArray[index - 1] + sortedArray[index]) / 2
+  } else {
+    medianValue = sortedArray[index]
+  }
+
+  return medianValue
+}

src/index.js

@@ -48,6 +48,7 @@ import contains from './contains'
 import getOrdinalSuffix from './get-ordinal-suffix'
 import arrayAverage from './array-average'
 import find from './find'
+import median from './array-median'
 
 export {
   isOdd,
@@ -100,4 +101,5 @@ export {
   contains,
   getOrdinalSuffix,
   arrayAverage,
+  median,
 }

test/array-median.test.js

@@ -0,0 +1,37 @@
+import test from 'ava'
+import {median} from '../src'
+
+test('accepts only typeof array param', t => {
+    const array = {}
+    const expected = `${array} is not an array.`
+    const actual = median(array)
+    t.deepEqual(actual, expected)
+})
+
+test('accepts only arrays with numeric items', t => {
+    const array = ['hello', 'world', 5, false]
+    const expected = `${array} contains non-numeric items.`
+    const actual = median(array)
+    t.deepEqual(actual, expected)
+})
+
+test('accepts only nonempty arrays', t => {
+    const array = []
+    const expected = `${array} has no items.`
+    const actual = median(array)
+    t.deepEqual(actual, expected)
+})
+
+test('finds the median of an array with odd number of items', t => {
+    const array = [13, 2, 5]
+    const expected = 5
+    const actual = median(array)
+    t.deepEqual(actual, expected)
+})
+
+test('finds the median of an array with even number of items', t => {
+  const array = [9, 25, 4, 1]
+  const expected = 6.5
+  const actual = median(array)
+  t.deepEqual(actual, expected)
+})