Lodash Map only on a Condition

Question

I have a file called events.json which I require then use .map to create my object,

var data = require('./events.json')
var newEventList = data.events.map(events => ({
    id: events.id ,
    name: events.name ,
    venue: events.venue.name
}));

However, sometimes on occasion I get two event.ids which are identical. In these instances the map method creates a duplicate entry in my newEventList object. Can I set a conditional within the map function to skip the 'mapping' of that entry if the ids are identical?

One thing to add is that the duplicates always are consecutive in the events.json so the If statement would only be comparing the previously mapped item.

Thanks for your help.

Why dont you filter the `data.events` first , before mapping , say using `_.unique()` ? — Malice, Dec 19 '17 at 13:37
I've never heard of this method before. Thanks I will take a look. — Bwizard, Dec 19 '17 at 13:40
https://stackoverflow.com/questions/31740155/lodash-remove-duplicates-from-array — Bwizard, Dec 19 '17 at 13:42

score 2 · Accepted Answer · answered Dec 19 '17 at 13:47

2

Use _.uniqBy available in lodash (Assuming OP wants a loadash solution)

 var data = require('./events.json');
 var _ = require('lodash')
 var newEventList = _.uniqBy(data.events,'id').map(events => ({
     id: events.id ,
     name: events.name ,
    venue: events.venue.name  
 }));

answered Dec 19 '17 at 13:47

Malice

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2 very similar answers here but am going to take this one as I like the way it is all contained in one function. Thanks – Bwizard Dec 19 '17 at 13:57

score 1 · Answer 2 · answered Dec 19 '17 at 13:45

Since you are using lodash, you can use the _.uniqBy function that lets you remove duplicates in an array :

const data = require('./events.json');
const uniqEvents = _.uniqBy(data.events, 'id');
const newEventList = uniqEvents.map(events => 
   id: events.id ,
   name: events.name ,
   venue: events.venue.name
);

score 1 · Answer 3 · answered Dec 19 '17 at 13:56

Array#map creates an output for every item in the original array, so you can't skip items. You can use Array#reduce instead with a helper dedupe Set. For each item, check if the id is in the Set. If not, add it to the result array, and to the Set.

const data = require('./events.json')
const dedupe = new Set();
const newEventList = data.events.reduce((list, event) => {
  if(!dedupe.has(event.id)) {
    list.push({
      id: event.id ,
      name: event.name ,
      venue: event.venue.name
    });

    dedupe.add(event.id);
  }

  return list;
}, []);

score 0 · Answer 4 · answered Dec 19 '17 at 13:45

0

var idList = [];
var data = require('./events.json')
var newEventList = data.events.map(events => {
idList.indexOf(events.id) !== -1 return // If id exists, skip
idList.push(events.id); // Else push in list for comparing 
return { // And add obj to array
    id: events.id ,
    name: events.name ,
    venue: events.venue.name
}
});

answered Dec 19 '17 at 13:45

Mosè Raguzzini

15,399
1
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1

Thanks for a non-lodash answer too! – Bwizard Dec 19 '17 at 13:58

Lodash Map only on a Condition

4 Answers4