Combine array elements into an object with a specific key in Javascript

I have a set of data structured as follows:

[{ team: 'Team1',
     wins: 1,
     group: GroupA
},{ team: 'Team2',
     wins: 1,
     group: GroupA
},{ team: 'Team3',
     wins: 1,
     group: GroupB
},{ team: 'Team4',
     wins: 1,
     group: GroupB
}]

My goal is to transform this data into a new format where it is grouped by a certain value, such as "group", and that value serves as a key in an object containing arrays:

{ GroupA: [{'Team1', wins: 1, group: GroupA},{'Team2', wins: 1, group: GroupA}],
GroupB: [{'Team3', wins: 1, group: GroupB},{'Team4', wins: 1, group: GroupB}]
}

Can anyone provide guidance on how I can achieve this?

I attempted the following approach which almost worked, but ended up returning objects instead:

var newStats = {}
     arrTeamStats.map(function(key,idx){

                var arr = [];

                if(newStats[key.group] == undefined) {
                    arr = key;
                    newStats[key.group] = arr;
                } else {
                else {
                    group = key.group;
                    newStats[group].push(key);
                }
           }
javascriptarraysobject

Answer №1

To convert your array into an Object, you can use the reduce method with a function.

arrTeamStats.reduce(function(h, o) {
  h[o.group] = h[o.group] || []
  h[o.group].push(o)
  return h
}, {})

Hope this helps!

Answer №2

You have a misconception about the .map() method. It is not a general iterator but rather designed to create a new array based on an existing one.

If you want to iterate over and add new properties to an object while consolidating the content, you can do so like this:

var data = [{ team: 'Team1', wins: 1, group: "GroupA"}, { team: 'Team2', wins: 1, group: "GroupA"},{ team: 'Team3',wins: 1,group: "GroupB"},{ team: 'Team4',wins: 1,group: "GroupB"}];

var result = {};
for (const o of data) {
  if (result.hasOwnProperty(o.group)) 
    result[o.group].push([o]);
  else 
    result[o.group] = [[o]];
}

console.log(result);

Alternatively, you can achieve similar results more succinctly with this code:

var data = [{ team: 'Team1', wins: 1, group: "GroupA"}, { team: 'Team2', wins: 1, group: "GroupA"},{ team: 'Team3',wins: 1,group: "GroupB"},{ team: 'Team4',wins: 1,group: "GroupB"}];

var result = {};
for (const o of data) 
  result[o.group] = (result[o.group] || []).concat([[o]]);

console.log(result);

Answer №3

If you're considering utilizing a library like Underscore, you can employ _.groupBy in the following manner:

var data = [{ name: 'Alice',
     age: 30,
     category: 'Category1'
},{ name: 'Bob',
     age: 25,
     category: 'Category2'
},{ name: 'Charlie',
     age: 35,
     category: 'Category1'
},{ name: 'David',
     age: 40,
     category: 'Category2'
}];

var result = _.groupBy(data, 'category');
console.log(result);
<script src="https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.13.7/underscore-min.js"></script>

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