replace duplicates in an array with new values from object

Question

I'm trying to "flatten" an array that has multiple duplicate values. The array is created from a CSV that I'm then trying to run API requests on. The format of the CSV is as follows:

Posts | Comments | 
post1   comment1
post1   comment2
post1   comment3
post2   comment1
post2   comment2
post2   comment3

I'm using Papaparse which returns:

[{Post: 'post1', Comment: 'comment1'}, {Post: 'post1', Comment: 'comment2'}, ...]

So I thought I would try to flatten them to where it would look like:

[{Post: 'post1', {Comment: 'comment1'}, {Comment: 'comment2'}}]

I tried using a .map and referencing the index to check if the previous Post was the same as the current Post if it is then .push to the previous index which I can't do using .map

What would be the correct way of doing this?

This is not valid json. You can have a comments array for each object? — Majed Badawi
– Majed Badawi, Commented Jun 28, 2022 at 19:58
I don't need it to be valid JSON I just need it to where I can run requests on each object. My api returns a new ID for the created Post, which I need access to so that I can create the Comments. When they are in separate objects, it makes that very difficult to do. — Dylan L.
– Dylan L., Commented Jun 28, 2022 at 20:02
Is this a good format? [ { "Post": "post1", "Comments": [ "comment1", "comment2", "comment3" ] } ... ] — Majed Badawi
– Majed Badawi, Commented Jun 28, 2022 at 20:05

Majed Badawi · Accepted Answer · 2022-06-28 20:08:05Z

1

Using Array#reduce, iterate over the list while updating a Map where the Post is the key and the value is an object with Post and grouped Comments array for the Post
Using Map#values, you can get a list of grouped objects

const data = [ { Post: 'post1', Comment: 'comment1' }, { Post: 'post1', Comment: 'comment2' }, { Post: 'post1', Comment: 'comment3' }, { Post: 'post2', Comment: 'comment1' }, { Post: 'post2', Comment: 'comment2' }, { Post: 'post2', Comment: 'comment3' } ];

const res = [...
  data.reduce((map, { Post, Comment }) => {
    const { Comments = [] } = map.get(Post) ?? {};
    map.set(Post, { Post, Comments: [...Comments, Comment] });
    return map;
  }, new Map)
  .values()
];

console.log(res);

answered Jun 28, 2022 at 20:08

Majed Badawi

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