Count iterations of an object array property in an array of objects

I am making a lottery system to practice javascript and react.

I am having a hard time creating a function that will check my betObject array for the most common bet combination and list each bet featuring this combination(to make a sum of the bet amounts later).

Bets come in two types : pair and shuffle. Pair bets have a combination of 2 numbers while shuffle bets have a combination of 3 to 6 numbers. Result of the draw is a 2 number combination.

I have tried using filter, map and equations to make this work, I am trying to make use of a For loop but I can't see how to use it to help with my problem.I have also tried pasing the bet.combination to an Int or a String without success.

the betObject array is structured as follows :

Here is my function so far :

const betsWatchList = () => {
    // Create watchlist array to store common bets array
    let watchlist = [];
    // loop through watchlist 
    for(let j = 0; j < watchlist.length; j++){
        //map through betList
        betList.map((bet, i) => {
            // if betlist combination matches watchlist
            if (watchlist[j].combination == bet.combination){
                // create new watchobject based on original
                let watchObject = {
                    combination : bet.combination,
                    total : watchlist[j].combination + bet.betTotal,
                    count : watchlist[j].count++
                }
                //replace original by updated
                watchlist.splice(j, watchObject);
            }else{
                //create new watchobject
                let watchObject = {
                    combination : bet.combination,
                    total : bet.betTotal,
                    count: 1
                }
                //push new watchobject
                watchlist.push(watchObject)
            }
        })
    } 
};

How would you approach this problem ? What should I change about my approach to find the solution faster ?

Thank you !

Don't use == to test whether two arrays contain identical values

Try replacing

 if (watchlist[j].combination == bet.combination)

with

  if (JSON.stringify(watchlist[j].combination) == JSON.stringify(bet.combination))

Instead of .splice, why not just write to the array element?

The code has a missing 1,. It should read .splice(j, 1, watchObject). However, it is all unnecessarily complicated, and doesn't actually need a .splice as we are not changing the number of elements.

Replace

watchlist.splice(j, watchObject); 

with

watchlist[j]= watchObject;

There was no reason to use .map

.map makes the programmer expect the code loop to return a result, when we could have used .forEach which makes it clear that it will not.

The loops are in reverse order

You need the outer loop to be over the bets. For each bet, you want the inner loop to examine each item in the watchList.

Just for simplicity, I have used .forEach

This avoids having to create and increment an iterator i.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

function betsWatchList(betList) {
  const watchList = [];
  betList.forEach(bet => {
    let found = false;

    // If already exists in watchList: update
    watchList.forEach((watchItem, j) => {
      if (JSON.stringify(watchItem.combination) === JSON.stringify(bet.combination)) {
        watchItem.total += bet.betTotal
        watchItem.count += 1
        found = true
      }
    });


    // If doesn't exist in watchList, append new watchList entry
    if (!found) {
      watchList.push({
        combination: bet.combination,
        total: bet.betTotal,
        count: 1
      });
    }

  })

  return watchList
}


const betList = [{
  combination: [1, 2, 3],
  betTotal: 10
}, {
  combination: [1, 2, 3],
  betTotal: 20
}, {
  combination: [1, 2, 4],
  betTotal: 10
}]

console.log(betsWatchList(betList))

<!-- end snippet -->