Add and join doubles in an array of objects

January 2, 2023

I hold all the expenses data in a JS Object as shown…

var transactions = {
  "date": "1-1-2023",
  "amount": "850",
  "name": "rent",
  "category": "housing",
  "notepad": ""
},
{
  "date": "1-1-2023",
  "amount": "91",
  "name": "electric",
  "category": "housing",
  "notepad": ""
},
{
  "date": "1-1-2023",
  "amount": "gas",
  "name": "83",
  "category": "housing",
  "notepad": ""
},
{
  "date": "1-1-2023",
  "amount": "50",
  "name": "car insurance",
  "category": "transportation",
  "notepad": ""
}

How can I calculate and all all the money together spent in housing and put it in an array (same with the other categories)?

The goal is to have something like …

var groups = ['housing', 'transportation']
var expenses = ['1000', '50']

>Solution :

Could you do something like this?

const transactions = [
  {
    date: "1-1-2023",
    amount: "850",
    name: "rent",
    category: "housing",
    notepad: "",
  },
  {
    date: "1-1-2023",
    amount: "91",
    name: "electric",
    category: "housing",
    notepad: "",
  },
  {
    date: "1-1-2023",
    amount: "83",
    name: "gas",
    category: "housing",
    notepad: "",
  },
  {
    date: "1-1-2023",
    amount: "50",
    name: "car insurance",
    category: "transportation",
    notepad: "",
  },
];

/**
 * This function calculates the expenses total for each category in the transactions array
 * @param transactions
 * @returns { expenseGroups: [string], expenseTotals: [number] }
 * @example
 */
function calculateExpenses(transactions) {
  const expenseGroups = [];
  const expenseTotals = [];

  transactions.forEach((transaction) => {
    const { category, amount } = transaction;
    const index = expenseGroups.indexOf(category);

    if (index === -1) {
      expenseGroups.push(category);
      expenseTotals.push(Number(amount));
    } else {
      expenseTotals[index] += Number(amount);
    }
  });

  return { expenseGroups, expenseTotals };
}

console.log({ result: calculateExpenses(transactions) });