Add sum of object after specific filter in array

Question

I want to add sum of first, second and third place to all teams after filtering the basic data.
But I am stuck with data which I want to push and I don't know how to fix this. Every time when function find a team with first position on specific season I want to add this fact to table medalTables to specific team f.e in season 2012 Barca was first and I want to add this to {team: Barca, first: 1} etc. (data are only example)

Code:

let medalTeams = [{
  name: "Real",
  first: 0,
  second: 0,
  third: 0
},{
  name: "Barca",
  first: 0,
  second: 0,
  third: 0
},{
  name: "Atletico",
  first: 0,
  second: 0,
  third: 0
}
 ]

  const medals = tables
    .filter((team) => (team.position === 1 || team.position === 2 || team.position === 3))
    .map((team, index) => {
        if(team.position === 1)
        medalTeams.filter(team => team.name === team.club).push({first: 1})
     
    });

What I want to reach:

/*
let medalTeams = [{
  name: "Real",
  first: 3,
  second: 1,
  third: 0
},{
  name: "Barca",
  first: 1,
  second: 2,
  third: 1
},{
  name: "Atletico",
  first: 0,
  second: 1,
  third: 3
}
 ]
 */

Basic data:

const tables = [
  {
    season: 2011,
    position: 1,
    club: 'Real'
  },
  {
    season: 2011,
    position: 2,
    club: 'Barca'
  },
  {
    season: 2011,
    position: 3,
    club: 'Atletico'
  },
    {
    season: 2012,
    position: 2,
    club: 'Real'
  },
  {
    season: 2012,
    position: 1,
    club: 'Barca'
  },
  {
    season: 2012,
    position: 3,
    club: 'Atletico'
  },
    {
    season: 2013,
    position: 1,
    club: 'Real'
  },
  {
    season: 2013,
    position: 3,
    club: 'Barca'
  },
  {
    season: 2013,
    position: 2,
    club: 'Atletico'
  },
    {
    season: 2014,
    position: 1,
    club: 'Real'
  },
  {
    season: 2014,
    position: 2,
    club: 'Barca'
  },
  {
    season: 2014,
    position: 3,
    club: 'Atletico'
  },
]

Mr. Polywhirl · Accepted Answer · 2021-01-26 14:10:11Z

Use a switch for the position and increment either the first, second, or third place field.

const tables = [
  { season: 2011 ,  position: 1 , club: 'Real'     },
  { season: 2011 ,  position: 2 , club: 'Barca'    },
  { season: 2011 ,  position: 3 , club: 'Atletico' },
  { season: 2012 ,  position: 2 , club: 'Real'     },
  { season: 2012 ,  position: 1 , club: 'Barca'    },
  { season: 2012 ,  position: 3 , club: 'Atletico' },
  { season: 2013 ,  position: 1 , club: 'Real'     },
  { season: 2013 ,  position: 3 , club: 'Barca'    },
  { season: 2013 ,  position: 2 , club: 'Atletico' },
  { season: 2014 ,  position: 1 , club: 'Real'     },
  { season: 2014 ,  position: 2 , club: 'Barca'    },
  { season: 2014 ,  position: 3 , club: 'Atletico' }
];

let medalTeams = [
  { name: "Real"     , first: 0 , second: 0 , third: 0 },
  { name: "Barca"    , first: 0 , second: 0 , third: 0 },
  { name: "Atletico" , first: 0 , second: 0 , third: 0 }
];

tables.forEach(entry => {
  const found = medalTeams.find(team => team.name === entry.club);
  switch (entry.position) {
    case 1: found.first++  ; break;
    case 2: found.second++ ; break;
    case 3: found.third++  ; break;
  }
});

console.log(medalTeams);

.as-console-wrapper { top: 0; max-height: 100% !important; }

You can make this more dynamic by adding the medal teams dynamically, based on the data.

const tables = [
  { season: 2011 , position: 1 , club: 'Real'     },
  { season: 2011 , position: 2 , club: 'Barca'    },
  { season: 2011 , position: 3 , club: 'Atletico' },
  { season: 2012 , position: 2 , club: 'Real'     },
  { season: 2012 , position: 1 , club: 'Barca'    },
  { season: 2012 , position: 3 , club: 'Atletico' },
  { season: 2013 , position: 1 , club: 'Real'     },
  { season: 2013 , position: 3 , club: 'Barca'    },
  { season: 2013 , position: 2 , club: 'Atletico' },
  { season: 2014 , position: 1 , club: 'Real'     },
  { season: 2014 , position: 2 , club: 'Barca'    },
  { season: 2014 , position: 3 , club: 'Atletico' }
];

const calculateMedals = (data) => {
  return data.reduce((result, entry) => {
    let team = result.find(existing => existing.name === entry.club);
    if (!team) {
      team = { name: entry.club, first: 0, second: 0, third: 0 };
      result.push(team);
    };
    switch (entry.position) {
      case 1: team.first++  ; break;
      case 2: team.second++ ; break;
      case 3: team.third++  ; break;
    }
    return result;
  }, []);
};

console.log(calculateMedals(tables));

.as-console-wrapper { top: 0; max-height: 100% !important; }

pilchard · Accepted Answer · 2021-01-28 16:08:39Z

This is really just a groupBy and sum situation.

Here is a general solution grouping by club and summing positions. It is a reduce() call, summing positions using position as key, and then remapping the positions to string keys.

const tables = [{ season: 2011, position: 1, club: 'Real' }, { season: 2011, position: 2, club: 'Barca' }, { season: 2011, position: 3, club: 'Atletico' }, { season: 2012, position: 2, club: 'Real' }, { season: 2012, position: 1, club: 'Barca' }, { season: 2012, position: 3, club: 'Atletico' }, { season: 2013, position: 1, club: 'Real' }, { season: 2013, position: 3, club: 'Barca' }, { season: 2013, position: 2, club: 'Atletico' }, { season: 2014, position: 1, club: 'Real' }, { season: 2014, position: 2, club: 'Barca' }, { season: 2014, position: 3, club: 'Atletico' },];

const byClub = Object.values(
  tables.reduce((a, { club, position, season }) => (
    (a[club] ??= { name: club, 1: 0, 2: 0, 3: 0 })[position] += 1, a), {})
).map(({ name, 1: first, 2: second, 3: third }) => ({ name, first, second, third }));

console.log(byClub);

Note: the snippet uses the lnullish assignment (??=) operator, but this can easily be replaced with a standard || short circuit.

(a[club] = a[club] || { 1: 0, 2: 0, 3: 0 })[position] += 1, a), {})

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