Javascript remove duplicate values from array of objects

Question

I've a requirement where the below array of objects should be converted to the result mentioned.

list = [{name : 'John', id : '1'}, {name : 'John', id : '2'}, {name : 'John', id : '3'}, {name : 'John', id : '4'}];

result to

list = [{name : 'John', id : '1, 2, 3, 4'}];

How can one do it?

• cst1992: Do you want the id to be a string or an array? i.e. '1,2,3,4' or ['1','2','3','4']?
• evolutionxbox: This is a duplicate of stackoverflow.com/questions/9229645/…
• Prateek Agarwal: It's a string with comma separated.

Answer 1

You could do it using a temporary object and Array#filter to filter out the duplicates and modify the original at the same time:

var list = [
 {name : 'John', id : '1'},
 {name : 'John', id : '2'},
 {name : 'John', id : '3'},
 {name : 'John', id : '4'}
 ],
 temp = {};
list = list.filter(function (o) {
 if (temp.hasOwnProperty(o.name)) {
 temp[o.name].id += ', ' + o.id;
 return false;
 }
 else {
 temp[o.name] = o;
 return true;
 }
});
document.body.textContent = JSON.stringify(list);

• Prateek Agarwal: How is it modifying the original list?
• Prateek Agarwal: Okay, now I get it. You are working with the o. Thanks!
• Andy E: @PrateekAgarwal: your welcome. Don't forget to accept the answer that works best for you :-).

Answer 2

This is to solve your specific question rather than a more general solution

function consolidate(list){
 var names={};
 list.forEach(function(e){
 if (!names[e.name]) names[e.name]=[e.id];
 else names[e.name].push(e.id);
 });
 var rtn=[];
 Object.keys(names).forEach(function(n){
 rtn.push({name:n, id:names[n].join(', ')});
 });
 return rtn;
}

basically use an object to accumulate the data then remap back into an array.

• Nina Scholz: why map? it does not return something.
• Euan Smith: Good point. This is really just my lazyness in typing, but you are correct and I've changed it to forEach

Answer 3

You can group it in a single loop with the help of a temoprary object without mutating the original array.

var list = [{ name: 'John', id: '1' }, { name: 'John', id: '2' }, { name: 'John', id: '3' }, { name: 'John', id: '4' }],
 grouped = [];
list.forEach(function (a) {
 if (!this[a.name]) {
 this[a.name] = { data: { name: a.name }, array: [] };
 grouped.push(this[a.name].data);
 }
 this[a.name].array.push(a.id);
 this[a.name].data.id = this[a.name].array.join(', ');
}, Object.create(null));
document.write('<pre>' + JSON.stringify(grouped, 0, 4) + '</pre>');

A slightly compacter version

var list = [{ name: 'John', id: '1' }, { name: 'John', id: '2' }, { name: 'John', id: '3' }, { name: 'John', id: '4' }],
 grouped = [];
list.forEach(function (a) {
 if (!this[a.name]) {
 this[a.name] = { name: a.name, id: a.id };
 grouped.push(this[a.name]);
 return;
 }
 this[a.name].id += ', ' + a.id;
}, Object.create(null));
document.write('<pre>' + JSON.stringify(grouped, 0, 4) + '</pre>');