JavaScript Reduce method in order to count object values with a specific keys reduced order method

I have an array like this:

const teamsPoints = [
  {team1_game00: 1},
  {team1_game01: 2},
  {team1_game02: 3},
  {team2_game00: 0},
  {team2_game10: 2},
  {team2_game11: 3},
  {team3_game01: 0},
  {team3_game10: 0},
  {team3_game20: 3},
  {team4_game02: 0},
  {team4_game11: 0},
  {team4_game20: 0}
]

What I'm trying to get is:

{
  team1: 6,
  team2: 5,
  team3: 3,
  team4: 0
}

which is the sum of points of every team.

I was trying to achieve that by using reduce method.

const scoreResult = teamsPoints.reduce((total, current) => {    

}, {});

As I understand I'm starting with an empty object, but then I have a problem to get proper key-value pairs (that's why I have not published it here, must admin reduce method is a kinda new thing to me).

Thank you in advance!

Answer:1

Here is a small sample using reduce. I basically get the name of the team, use it as a key in the reduced result and increment its value!

Hope this will help you ;) Feel free to ask me anything if it's not clear! 

const teamsPoints = [
{team1_game00: 1},
{team1_game01: 2},
{team1_game02: 3},
{team2_game00: 0},
{team2_game10: 2},
{team2_game11: 3},
{team3_game01: 0},
{team3_game10: 0},
{team3_game20: 3},
{team4_game02: 0},
{team4_game11: 0},
{team4_game20: 0}
];

const scoreResult = teamsPoints.reduce((total, game) => {
  const [gameName] = Object.keys(game);
  const [team] = gameName.split('_');
  total[team] = total[team] || 0;
  total[team] += game[gameName];
  return total;
}, {});

console.log(scoreResult);
Answer:2

You can use the function reduce to group the teams.

const teamsPoints = [{team1_game00: 1},{team1_game01: 2},{team1_game02: 3},{team2_game00: 0},{team2_game10: 2},{team2_game11: 3},{team3_game01: 0},{team3_game10: 0},{team3_game20: 3},{team4_game02: 0},{team4_game11: 0},{team4_game20: 0}],
      result = teamsPoints.reduce((a, c) => {
        let keys = Object.keys(c),
            [key] = keys[0].split('_');
        a[key] = (a[key] || 0) + c[keys[0]];
        return a;
      }, {});

console.log(result);
.as-console-wrapper { max-height: 100% !important; top: 0; }
Answer:3

So generally I wouldn't use reduce for this, just because of how the objects are organized. You wouldn't really want to signify what game and what team it is in the same object, but if you did have those objects like that I would first create a second object to store the totals, and do the following

let totals = {};

teamsPoints.map(obj => {
  Object.keys(obj).map(key => {
    if (totals.hasOwnProperty(key.split('_')[0])) {
       totals[key.split('_')[0]] += obj[key];
    } else {
      totals[key.split('_')[0]] = obj[key];
    }
  });
});
Answer:4

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