feat(reduceCount): added reduceCount function (#211)

* feat(reduceCount): added reduceCount function to count occurences of param in array(s)

* feat(reduceCount): removed history folder

Author: thall1961

src/index.js

@@ -77,6 +77,7 @@ import removeProperty from './removeProperty'
 import temperatureConverter from './temperatureConverter'
 import last from './last'
 import descendingOrder from './descending-order'
+import reduceCount from './reduceCount'
 
 export {
   reverseArrayInPlace,
@@ -158,4 +159,5 @@ export {
   temperatureConverter,
   last,
   descendingOrder,
+  reduceCount,
 }

src/reduceCount.js

@@ -0,0 +1,31 @@
+export default reduceCount
+
+/**
+ * Original Source: https://egghead.io/courses/reduce-data-with-javascript
+ *
+ * The function will count how many times an item occurs in an array,
+ * even in arrays within the array.
+ * @param  {array} array - The array
+ * @param  {any type} item - The variable whose occurences will be counted
+ * @return {number} - The amount of times the item is found in the array(s)
+ */
+
+function reduceCount(array, itemToCount) {
+  // make sure the array passed in is actually an array
+  if (!Array.isArray(array)) {
+    return `${array} isn't an array.`
+  }
+
+  // make sure we got something to work with in that array
+  if (array.length === 0) {
+    return `${array} is empty.`
+  }
+
+  // reduce the array and count the occurences of item
+  return array.reduce((a, b) => {
+    if (Array.isArray(b)) {
+      return a + reduceCount(b, itemToCount)
+    }
+    return a + (b === itemToCount ? 1 : 0)
+  }, 0)
+}

test/reduceCount.test.js

@@ -0,0 +1,37 @@
+import test from 'ava'
+import {reduceCount} from '../src'
+
+test('first param has to be an array', t => {
+  const array = {}
+  const expected = `${array} isn't an array.`
+  const actual = reduceCount(array, 0)
+  t.deepEqual(actual, expected)
+})
+
+test('array must have at least one value', t => {
+  const array = []
+  const expected = `${array} is empty.`
+  const actual = reduceCount(array, 0)
+  t.deepEqual(actual, expected)
+})
+
+test('array will count occurences of integer param', t => {
+  const array = [1, 2, [1, 3], 4, 5, [1, 6, 7]]
+  const expected = 3
+  const actual = reduceCount(array, 1)
+  t.deepEqual(actual, expected)
+})
+
+test('array will count occurences of string param', t => {
+  const array = ['six', 2, [1, 'six'], 4, 5, [1, 'six', 7], 'six', 'sicks']
+  const expected = 4
+  const actual = reduceCount(array, 'six')
+  t.deepEqual(actual, expected)
+})
+
+test('array will count occurences of float param', t => {
+  const array = [1, 2, [1, 3], 4, 6.4, [1, 6.4, 7], 6.4, 6.5, 4.6]
+  const expected = 3
+  const actual = reduceCount(array, 6.4)
+  t.deepEqual(actual, expected)
+})