how to create a new object from the sum of elements of an array of objects

Question

I am doing a data manipulation practice with an array of objects, which I want to add income and expenses of all the objects of the array and return an object, I do the sum in a "correct" way but it is dirty and I would like to know If there is a cleaner way to do the code.
This is the array of objects:

const projects = [
  {
    amount: 26800,
    type: 'expense',
  },
  {
    amount: 2600,
    type: 'income',
  },
  {
    amount: 6890,
    type: 'expense',
  },
  {
    amount: 901800,
    type: 'expense',
  },
  ...
];

This my code javascript:

const dato = () => {
  let income = 0;
  let expense = 0;
  const total = projects.map((project) => {
    income += project.type === 'income' ? project.amount : 0;
    expense += project.type === 'expense' ? project.amount : 0;
    return {
      income,
      expense,
      byTotal: {
        total: income - expense,
      },
    };
  });

  console.log(total[total.length - 1]);
};

The object I want to create is the following.

{
  income: 3900000,
  expense: 2293600,
  byTotal: {
    total: 1606400,
  }
}

you can also use reduce

cmgchess
– cmgchess

2022-07-14 06:34:10 +00:00
Commented Jul 14, 2022 at 6:34 — cmgchess
– cmgchess, Commented Jul 14, 2022 at 6:34

trincot · Accepted Answer · 2022-07-14 06:39:59Z

1

You can use reduce instead of map, and use Object.assign to sum the amounts in an accumulator object:

const projects = [{amount: 26800,type: 'expense',},{amount: 2600,type: 'income',},{amount: 6890,type: 'expense',},{amount: 901800,type: 'expense',},];

const dato = () => {
    const {income, expense} = projects.reduce(
        (acc, {type, amount}) => Object.assign(acc, {[type]: acc[type] + amount}),
        {income: 0, expense: 0}
    );
    const total = {income, expense, byTotal: {total: income - expense}};
    console.log(total);
};

dato();

answered Jul 14, 2022 at 6:39

trincot

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Comments

iamhuynq · Accepted Answer · 2022-07-14 06:40:10Z

1

You can use reduce

const total = projects.reduce(
    (acc, cur) => {
        if (cur.type == 'income') acc.income += cur.amount;
        if (cur.type == 'expense') acc.expense += cur.amount;
        acc.byTotal.total += acc.income - acc.expense;
        return acc;
    },
    {
        income: 0,
        expense: 0,
        byTotal: {
            total: 0,
        },
    }
);

answered Jul 14, 2022 at 6:40

iamhuynq

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Comments

rjumatov · Accepted Answer · 2022-07-14 06:35:16Z

0

You can make use of a reducer by subtracting or adding the amount based on the type in one line:

const projects = [{
    amount: 26800,
    type: 'expense',
  },
  {
    amount: 2600,
    type: 'income',
  },
  {
    amount: 6890,
    type: 'expense',
  },
  {
    amount: 901800,
    type: 'expense',
  }
];

const sum = projects.reduce(
  (amount, object) =>
  amount + (object.type === "expense" ? -object.amount : object.amount),
  0
);

console.log(sum)

answered Jul 14, 2022 at 6:35

rjumatov

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