Filtering an array with another array and creating new objects?

Question

I have an object(array?) called expenses, each expense inside has a description, amount and user(displayName).. I went through the expenses object and got all the unique users (uniqueNames)... now I want to create new objects that contain expenses for just each user.


const uniqueNames = [];
  // Get unique names from my state.expenses
  state.expenses.map((expense) => {
    if (uniqueNames.indexOf(expense.displayName) === -1) {
      uniqueNames.push(expense.displayName);
    }
  });

// Unique names now contains 2 names, as expected

// not sure how to do this next part, it outputs nothing and gives me no errors.
  const myExpenses = [];
  uniqueNames.map((name) => {
    state.expenses
      .filter((expense) => {
        expense.displayName.includes(name);
      })
      .map((expense) => {
        myExpenses.push(expense.description);
      });
  });
  console.log("unique names", uniqueNames);
// unique names contains my 2 names of users found in the expense array

  console.log("my expenses by names", myExpenses);
// myExpenses is empty ?

Orelsanpls · Accepted Answer · 2020-12-16 08:56:33Z

1

Look at the following :

First we use the Set utility class to create an array of unique user names.

Then, we loop on the uniqueNames in order to create a new array using map, and build up the expenses for each user using reduce, to do the sum of every amounts.

const state = {
  expenses: [{
    displayName: 'foo',
    description: 'snake',
    amount: 5,
  }, {
    displayName: 'bar',
    description: 'cat',
    amount: 2,
  }, {
    displayName: 'bar',
    description: 'dog',
    amount: 8,
  }],
};

const uniqueNames = Array.from(state.expenses.reduce((tmp, {
  displayName,
}) => tmp.add(displayName), new Set()));

console.log('The unique names', uniqueNames);

const expenses = uniqueNames.map(x => ({
  name: x,

  expense: state.expenses.reduce((tmp, {
    displayName,
    amount,
  }) => displayName === x ? tmp + amount : tmp, 0),
}))

console.log('My expenses by names', expenses);

answered Dec 16, 2020 at 8:56

Orelsanpls

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1 Comment

MrVerticalStack Over a year ago

That worked freaking perfectly. THANK YOU SO MUCH!! :D

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