Add scores of array with objects that have the same ID

Question

I have an array of objects:

console.log(quizNight[0].round[--latestRound].t)
 -> [ { teamID: 16867, correctAnswers: 1 },
      { teamID: 16867, correctAnswers: 1 },
      { teamID: 16867, correctAnswers: 1 } ]

and I want to have a correctTotalAnswers array to look like this:

[ { teamID: 16867, correctTotalAnswers: 3} ]

What would be the smartest way to go about it? The code which I have now:

let correctAnswersArrayRoung = quizNight[0].round[--latestRound].t;
let totalCorrentAnswersArray = [];
for (let correctAnswer in correctAnswersArrayRoung) {
   console.log(correctAnswersArrayRoung[correctAnswer])
   for(let element in totalCorrentAnswersArray){
      if(element.teamID === correctAnswer.teamID){
         element.totalCorrectAnswers = ++element.totalCorrectAnswers
      } else {
         totalCorrentAnswersArray.push({
            teamID: correctAnswer.teamID,
            totalCorrectAnswers: 1
         })
      }
   }
}
console.log(totalCorrentAnswersArray)

this returns []

Answer 1

You can use reduce this way (see the inline comments):

 // Your initial data const initialArray = [ { teamID: 16867, correctAnswers: 1 }, { teamID: 16867, correctAnswers: 1 }, { teamID: 16866, correctAnswers: 1 } ] // Use reduce to loop through the data array, and sum up the correct answers for each teamID let result = initialArray.reduce((acc, c) => { // The `acc` is called "accumulator" and it is // your object passed as the second argument to `reduce` // We make sure the object holds a value which is // at least `0` for the current team id (if it exists, // it will be used, otherwise will be initialized to 0) acc[c.teamID] = acc[c.teamID] || 0 // Sum up the correctAnswers value acc[c.teamID] += c.correctAnswers return acc }, {}) // <- Start with an empty object // At this point the result looks like this: // { // "16866": 1, // "16867": 2 // } // Finally convert the result into an array result = Object.keys(result).map(c => ({ teamID: c, correctAnswers: result[c] })) console.log(result);