merge two arrays of strings to an array of objects

Question

I have two arrays that look like this:

const players = ["id1", "id2", "id3", "id4"]
const games = ["gid1", "gid2"]

I need to return an array that looks like this:

const newArray = [
  {playerId: "id1", gameId: "gid1"}, {playerId: "id1", gameId: "gid2"},
  {playerId: "id2", gameId: "gid1"}, {playerId: "id2", gameId: "gid2"},
  {playerId: "id3", gameId: "gid1"}, {playerId: "id3", gameId: "gid2"},
  {playerId: "id4", gameId: "gid1"}, {playerId: "id4", gameId: "gid2"}
]

What's the best way to achieve this? I have been trying a combination of map and reduce, but can't seem to figure it out.

@charlietfl: Looks like a cartesian product. But would be good if it said. — T.J. Crowder
– T.J. Crowder, Commented Nov 26, 2017 at 19:12
"I have been trying a combination of map and reduce, but can't seem to figure it out." Show us that. Separately: Why reach for something complicated when nested loops will do the job nicely? — T.J. Crowder
– T.J. Crowder, Commented Nov 26, 2017 at 19:13

RomanPerekhrest · Accepted Answer · 2017-11-26 19:14:46Z

3

With Array.reduce() and Array.forEach() functions:

const players = ["id1", "id2", "id3", "id4"]
const games = ["gid1", "gid2"]

const result = players.reduce((r, p_id) => {
    games.forEach((g_id) => r.push({playerId: p_id, gameId: g_id}));
    return r;
}, []);

console.log(result);

answered Nov 26, 2017 at 19:14

RomanPerekhrest

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Comments

Emre Kabaoglu · Accepted Answer · 2017-11-26 19:15:48Z

3

You want to create cartesian array. You can perform it like this;

var newArray = [];
for (var i = 0; i < players.length; i++) {
    for (var l = 0; l < games.length; l++) {
        var merged = {playerId: players[i], gameId: games[l]};
        newArray.push(merged);
    }
}

answered Nov 26, 2017 at 19:15

Emre Kabaoglu

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Comments

scroobius · Accepted Answer · 2017-11-26 19:21:16Z

1

Here's a solution using es6 for...of

const players = ['id1', 'id2', 'id3', 'id4']
const games = ['gid1', 'gid2']
let newArray = []

for (let game of games) {
   for (let player of players) {
       newArray.push({playerId: player, gameId: game})
       }
    }

answered Nov 26, 2017 at 19:21

scroobius

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Comments

Andy · Accepted Answer · 2017-11-26 19:57:44Z

0

Here's a different take on the functional approach which breaks down the code into smaller parts:

const players = ["id1", "id2", "id3", "id4"]
const games = ["gid1", "gid2"];

const flatten = arrs => [].concat(...arrs);
const getGame = (id, gid) => ({ playerId: id, gameId: gid });
const getGames = games => id => games.map(gid => getGame(id, gid));
const output = flatten(players.map(getGames(games)));

console.log(output)

answered Nov 26, 2017 at 19:57

Andy

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