clear reduce example

reduce.js

let footballPlayers = [{
        gender: "M",
        name: "Karim Benzema",
        age: 29,
        club: "Real Madrid CF",
        country: "Spain"
    },
    {
        gender: "M",
        name: "Samir Nasri",
        age: 29,
        club: "Sevilla FC",
        country: "Spain"
    },
    {
        gender: "M",
        name: "Hatem Ben Arfa",
        age: 29,
        club: "PSG",
        country: "France"
    },
    {
        gender: "M",
        name: "Radamel Falcao",
        age: 27,
        club: "AS Monaco FC",
        country: "France"
    },
    {
        gender: "M",
        name: "Riyad Mahrez",
        age: 25,
        club: "Leicester City FC",
        country: "England"
    },
    {
        gender: "M",
        name: "Sofiane Feghouli",
        age: 26,
        club: "West Ham United",
        country: "England"
    }
];

let playersByCountry = footballPlayers.reduce((players, player, index) => {

    if (player.country === "France") {
        players.france.push(player)
    } else if (player.country === "England") {
        players.england.push(player)
    } else if (player.country === "Spain") {
        players.spain.push(player)
    }

    return players

}, {
    france: [],
    england: [],
    spain: []
});

console.dir(JSON.stringify(playersByCountry));

{
	"france": [{
		"gender": "M",
		"name": "Hatem Ben Arfa",
		"age": 29,
		"club": "PSG",
		"country": "France"
	}, {
		"gender": "M",
		"name": "Radamel Falcao",
		"age": 27,
		"club": "AS Monaco FC",
		"country": "France"
	}],
	"england": [{
		"gender": "M",
		"name": "Riyad Mahrez",
		"age": 25,
		"club": "Leicester City FC",
		"country": "England"
	}, {
		"gender": "M",
		"name": "Sofiane Feghouli",
		"age": 26,
		"club": "West Ham United",
		"country": "England"
	}],
	"spain": [{
		"gender": "M",
		"name": "Karim Benzema",
		"age": 29,
		"club": "Real Madrid CF",
		"country": "Spain"
	}, {
		"gender": "M",
		"name": "Samir Nasri",
		"age": 29,
		"club": "Sevilla FC",
		"country": "Spain"
	}]
}