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July 20, 2022 07:38 am GMT

Calling all beginners: solution to part II's homework

Hello, coders!

In the previous episode of this beginners series I gave you an exercise based on the following initial data:

const purchases = [    {item: 'socks', amount: 25.98, date: '2022-05-07 09:31:29'},    {item: 'jacket', amount: 145.98, date: '2022-05-17 17:01:09'},    {item: 'cap', amount: 12.99, date: '2022-05-17 17:03:12'},    {item: 'socks', amount: 43.99, date: '2022-06-11 18:24:16'},    {item: 'cap', amount: 13.99, date: '2022-06-11 18:24:16'},    {item: 'jacket', amount: 132.99, date: '2022-06-21 11:21:35'},    {item: 'socks', amount: 13.99, date: '2022-06-23 09:43:28'},    {item: 'socks', amount: 12.99, date: '2022-07-01 13:14:56'},    {item: 'jacket', amount: 132.99, date: '2022-07-03 15:24:24'},    {item: 'cap', amount: 32.99, date: '2022-07-05 11:14:15'},    {item: 'socks', amount: 13.99, date: '2022-07-07 11:14:15'},];

Create a list of best and worst selling items of each month.
Best and worst are defined by the revenue they generated.

Expected result:

const topFlops = {  "2022-05": {    top: 'jacket',    flop: 'cap'  },  "2022-06": {    top: 'jacket',    flop: 'cap'  },  "2022-07": {    top: 'jacket',    flop: 'socks'  }}

Let's see how we could go about implementing a solution.

Step by step solution

First, let's write in plain English what we need to do:

  1. group purchases by month and items
  2. get first and last item of each month and make them top and flop

Sounds good. Let's write our code outline.

const purchases = [ /* omitted for readability */];const itemsMonthlyRevenue = getItemsMonthlyRevenue(purchases);const topFlop = getTopFlopFromMonthlyRevenue(itemsMonthlyRevenue);

getItemsMonthlyRevenue

getItemsMonthlyRevenue needs to add one level compared to what we had in Part II's first exercise to store items' monthly revenue.

const getItemsMonthlyRevenue = (purchases) => {    let monthlyRevenue = {}    purchases.forEach(function (purchase) {        const purchaseDate = purchase.date.substring(0, 7);        if (monthlyRevenue[purchaseDate] === undefined) {            monthlyRevenue[purchaseDate] = {}        }        monthlyRevenue[purchaseDate][purchase.item] = purchase.amount + (monthlyRevenue[purchaseDate][purchase.item] || 0);    })    return monthlyRevenue;}const purchases = [ /* omitted for readability */];const itemsMonthlyRevenue = getItemsMonthlyRevenue(purchases);console.log(JSON.stringify(itemsMonthlyRevenue, null, 2));

The main difference with Part II's first exercise is that monthlyRevenue[purchaseDate] is now an object so we need to make sure it's initialized before accessing it.

Let's run it and see what we get in the console.

Output:

{  "2022-05": {    "socks": 25.98,    "jacket": 145.98,    "cap": 12.99  },  "2022-06": {    "socks": 57.980000000000004,    "cap": 13.99,    "jacket": 132.99  },  "2022-07": {    "socks": 26.98,    "jacket": 132.99,    "cap": 32.99  }}

Excellent. Onto getTopFlopFromMonthlyRevenue!

getTopFlopFromMonthlyRevenue

const getTopFlopFromMonthlyRevenue = (monthlyRevenue) => {    let topFlop = {};    const NAME_IDX = 0;    const REVENUE_IDX = 1;    for (let month in monthlyRevenue) {        // step 1: get an array of item/monthlyRevenue        const productsSales = Object.entries(monthlyRevenue[month]);        // step 2: sort by revenue        productsSales.sort(function (p1, p2) {            return p2[REVENUE_IDX] < p1[REVENUE_IDX] ? 1 : -1;        })        // step 3: fill the topFlop array object        topFlop[month] = ({            flop: productsSales[0][NAME_IDX],            top: productsSales[productsSales.length - 1][NAME_IDX]        })    }    return topFlop;}

What's going on here?
Each month holds a list of items as keys and revenue as values and that's what we want to sort.
I make use of Object.entries which returns an array of [key, value] tuples. Example:

console.log(monthlyRevenue['2022-06']);// outputs[  [ "socks", 57.980000000000004 ],  [ "cap", 13.99 ],  [ "jacket", 132.99 ],]

We can now sort that array and get the first and last element which will be out flop and top respectively.

Putting it all together

const getItemsMonthlyRevenue = (purchases) => {    let monthlyRevenue = {}    purchases.forEach(function (purchase) {        const purchaseDate = purchase.date.substring(0, 7);        if (monthlyRevenue[purchaseDate] === undefined) {            monthlyRevenue[purchaseDate] = {}        }        monthlyRevenue[purchaseDate][purchase.item] = purchase.amount + (monthlyRevenue[purchaseDate][purchase.item] || 0);    })    return monthlyRevenue;}const getTopFlopFromMonthlyRevenue = (monthlyRevenue) => {    let topFlop = {};    const NAME_IDX = 0;    const REVENUE_IDX = 1;    for (let month in monthlyRevenue) {        const productsSales = Object.entries(monthlyRevenue[month]);        productsSales.sort(function (p1, p2) {            return p2[REVENUE_IDX] < p1[REVENUE_IDX] ? 1 : -1;        })        topFlop[month] = ({            flop: productsSales[0][NAME_IDX],            top: productsSales[productsSales.length - 1][NAME_IDX]        })    }    return topFlop;}const purchases = [    {item: 'socks', amount: 25.98, date: '2022-05-07 09:31:29'},    {item: 'jacket', amount: 145.98, date: '2022-05-17 17:01:09'},    {item: 'cap', amount: 12.99, date: '2022-05-17 17:03:12'},    {item: 'socks', amount: 43.99, date: '2022-06-11 18:24:16'},    {item: 'cap', amount: 13.99, date: '2022-06-11 18:24:16'},    {item: 'jacket', amount: 132.99, date: '2022-06-21 11:21:35'},    {item: 'socks', amount: 13.99, date: '2022-06-23 09:43:28'},    {item: 'socks', amount: 12.99, date: '2022-07-01 13:14:56'},    {item: 'jacket', amount: 132.99, date: '2022-07-03 15:24:24'},    {item: 'cap', amount: 32.99, date: '2022-07-05 11:14:15'},    {item: 'socks', amount: 13.99, date: '2022-07-07 11:14:15'},];const itemsMonthlyRevenue = getItemsMonthlyRevenue(purchases);const topFlop = getTopFlopFromMonthlyRevenue(itemsMonthlyRevenue);console.log(JSON.stringify(topFlop, null, 2));

Hope it helps you, as a beginner, to see how to tackle a task.

Happy coding!


Original Link: https://dev.to/joolsmcfly/calling-all-beginners-solution-to-part-iis-homework-b8i

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