Manipulating arrays in JavaScript to remove repeat objects and total them up

Question

How would I take the following array in JavaScript

locationList = [{
  id: 1,
  title: "Loughborough"
}, {
  id: 5,
  title: "Corby"
}, {
  id: 2,
  title: "Derby"
}, {
  id: 2,
  title: "Derby"
}, {
  id: 2,
  title: "Derby"
}];

and convert it into something like this:

locationList = [{
  id: 1
  title: "Loughborough",
  count: 1
}, {
  id: 5
  title: "Corby",
  count: 1
}, {
  id: 2
  title: "Derby",
  count: 3
}];

wherein all the titles are totalled up.

create new array, loop through each element, if element.title is not in array, add to array, if it is and to count in specific index. Would have thought it would have been easy with a rep like yours :/ — thatOneGuy
– thatOneGuy, Commented Jan 22, 2016 at 11:11
I've been looking at the array.reduce function, but I just wanted another opinion — methuselah
– methuselah, Commented Jan 22, 2016 at 11:11
@daremachine who cares, just write the answer and enjoy the upvotes. — mahen23
– mahen23, Commented Jan 22, 2016 at 12:17

Derlin · Accepted Answer · 2016-01-22 12:29:30Z

4

One of many solutions:

var newl = [];
locationList.forEach(function(o) {
  if (newl[o.id] == undefined) {
    o.count = 1;
    newl[o.id] = o;
  } else {
    newl[o.id].count += 1;
  }
});

// if you want a trimmed array (with length = 3)
var trimedArray = newl.filter(function(n){ return n != undefined });

edited Jan 22, 2016 at 12:29

answered Jan 22, 2016 at 11:15

Derlin

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5 Comments

methuselah Over a year ago

Thanks. I tried this code, it works very well so I have selected it as the correct answer. However, at the end it tells me the length of my array is 6, when it should be 3. Do you know why this is happening? I think it is creating some empty array elements in the process.

Derlin Over a year ago

This is because id is actually an integer. The js runtime thinks newl is a regular array... You end up with an array with the biggest number + 1. To trim the array, you cane use: var trimedArray = newl.filter(function(n){ return n != undefined });

methuselah Over a year ago

Is there any way to remove the empty elements? I am having some rendering issues as a result: imgur.com/quuGXs9

gothical Over a year ago

This should create the array correctly: var newl = [],x = -1; locationList.forEach(function(o) { if (newl[o.id] == undefined) { x++; o.count = 1; newl[x] = o; } else { newl[x].count += 1; } });

Derlin Over a year ago

@gothical: your solution cannot work, since you use the id to check if the element is present, but x to index it...

Zhafur · Accepted Answer · 2016-01-22 11:15:01Z

2

Loop through the elements, create a new array, put an element into the new array if the element is not yet in.

Edit: Otherwise, if it exists, just add 1 to the count in the new array, and then use the new array instead of the old.

edited Jan 22, 2016 at 11:15

answered Jan 22, 2016 at 11:12

Zhafur

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Comments

thatOneGuy · Accepted Answer · 2016-01-22 11:13:46Z

1

As I have said in comments :

Create new array, loop through each element, if element.title is not in new array, add to array, if it is add to count in specific index

answered Jan 22, 2016 at 11:13

thatOneGuy

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