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:
- group purchases by month and items
- get first and last item of each month and make them
topandflop
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! ⌨️
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