How can I map an array with duplicate values to a unique array in Javascript?

Question

I have the following array:

var tst = 
[
 {"topicId":1,"subTopicId":1,"topicName":"a","subTopicName":"w"},
 {"topicId":1,"subTopicId":2,"topicName":"b","subTopicName":"x"},
 {"topicId":1,"subTopicId":3,"topicName":"c","subTopicName":"y"},
 {"topicId":2,"subTopicId":4,"topicName":"c","subTopicName":"z"}
]

Is there an easy way that I can map that to this kind of array where topicId > id and topicName > name:

var t = 
[
  {"id":1,"name":"a"},
  {"id":2,"name":"c"}
]

I am using a modern browser and I also have _lodash if that helps. Note that there will be about 100 rows in the tst array so I don't need a very optimized solution. A simple and easy to maintain solution would be more important.

Answer 1

MOST RECENT

_.uniqBy is now preferable

Full working example here

var tst = [
 {"topicId":1,"subTopicId":1,"topicName":"a","subTopicName1":"w"},
 {"topicId":2,"subTopicId":2,"topicName":"b","subTopicName2":"x"},
 {"topicId":3,"subTopicId":3,"topicName":"c","subTopicName3":"y"},
 {"topicId":1,"subTopicId":4,"topicName":"c","subTopicName4":"z"}
];

var result = _.map(_.uniqBy(tst, 'topicId'), function (item) {
    return {
        id: item.topicId,
        name: item.topicName
    };  
});

console.log(result);

---

LEGACY

http://lodash.com/docs#uniq is a good start

_.uniq([{ 'x': 1 }, { 'x': 2 }, { 'x': 1 }], 'x');

Your code would look like this to get topics unique by id

var t = _.uniq(tst, 'topicId');

EDIT

I made a jsfiddle

http://jsfiddle.net/q5HNw/

UPDATE

Removed unnecessary uniqueness of names

http://jsfiddle.net/q5HNw/1/

Answer 2

I am one of those guys that use native functions :)

var results = tst.reduce(function(res,topic){
var exists = res.some(function(t){ return (t.id === topic.topicId && t.name === topic.topicName);});        
     if (!exists){
        res.push({"id": topic.topicId, "name": topic.topicName});
     }
return res; },[]);

Lodash version

I am not an expert using lodash, probably I will try something like this:

var results = _.reduce(tst, function(res, topic){       
    var exists = _.findIndex(res, function(t){
        return (t.id === topic.topicId && t.name === topic.topicName);
    });
    if (exists === -1){
      res.push({"id": topic.topicId, "name": topic.topicName});
    }
    return res; 
},[]);

Answer 3

Using ECMAScript 2015 Array.prototype.find()

The find() method returns the value of the first element in the array that satisfies the provided testing function. Otherwise undefined is returned.

let tst = [
     {"topicId":1,"subTopicId":1,"topicName":"a","subTopicName":"w"},
     {"topicId":1,"subTopicId":2,"topicName":"b","subTopicName":"x"},
     {"topicId":1,"subTopicId":3,"topicName":"c","subTopicName":"y"},
     {"topicId":2,"subTopicId":4,"topicName":"c","subTopicName":"z"},
];

let t = [];
tst.forEach(obj => {
  // Check if the id already exists in the array 't'
  if (!t.find((self) => self.id === obj.topicId)) {
    // If not, pushes obj to t
    t.push({
      id: obj.topicId,
      name: obj.topicName
    });
  }
});

console.log(t);

You can also compare more than one property:

let tst = [
         {"topicId":1,"subTopicId":1,"topicName":"a","subTopicName":"w"},
         {"topicId":1,"subTopicId":2,"topicName":"b","subTopicName":"x"},
         {"topicId":1,"subTopicId":3,"topicName":"c","subTopicName":"y"},
         {"topicId":2,"subTopicId":4,"topicName":"c","subTopicName":"z"},
];


let t = [];
tst.forEach(obj => {
  // Check if the 'id' and 'subId' already exist in t 
  if (!t.find((self) => self.id === obj.topicId && self.subId === obj.subTopicId)) {
    // If not, pushes obj to t
    t.push({
      id: obj.topicId,
      subId: obj.subTopicId,
      name: obj.topicName
    });
  }
});

console.log(t);