node map and filter results into new array

Question

I'm having a brain fart, can someone point me in the right direction please.

Objective: Taking rows from a query, format the rows into new arrays of coordinates with ID as the index.

Example response from query: This is an array of objects, returned from mysql query. Cleared up possible confusion.

[
    {
        id: 2031,
      store_id: 12,
      latitude: '40.734479',
      longitude: '-73.998943' 
    },
    {
        id: 2041,
        store_id: 12,
      latitude: '40.732912',
      longitude: '-74.000083' 
    },
    {
        id: 2051,
      store_id: 14,
      latitude: '40.731053',
      longitude: '-74.001423' 
    },
    {
        id: 2061,
        store_id: 14,
        latitude: '40.729696',
        longitude: '-74.002186' 
    },
    {
        id: 2071,
        store_id: 14,
        latitude: '40.729121',
        longitude: '-74.002473' 
    }
]

Desired output:

{
    12:[
        { latitude: '40.734479', longitude: '-73.998943' },
        { latitude: '40.732912', longitude: '-74.000083' }
    ],

    14:[
        { latitude: '40.731053', longitude: '-74.001423'},
        { latitude: '40.729696', longitude: '-74.002186'},
        { latitude: '40.729121', longitude: '-74.002473'}
    ]
}

Previously, utilizing a for loop, I've checking if object had property, then creating property if not, then populated the arrays.

Is there a better way to achieve this with map and reduce and/or filter?

Thanks.

Agreed. Can you clarify if those objects you listed are part of an array? Or are they contained in some other type of structure? — CRice, Feb 13 '18 at 01:30
@GillesQuenot It's mysql query return. It's an array of objects. I just copied from console. -- I just cleared up the input to make this clear. — BardsWork, Feb 13 '18 at 01:30
Possible duplicate of [What is the most efficient method to groupby on a JavaScript array of objects?](https://stackoverflow.com/questions/14446511/what-is-the-most-efficient-method-to-groupby-on-a-javascript-array-of-objects) — Slai, Feb 13 '18 at 02:11

score 3 · Accepted Answer · answered Feb 13 '18 at 01:37

You can achieve this with Array.reduce:

const myArr = [{
  id: 2031,
  store_id: 12,
  latitude: '40.734479',
  longitude: '-73.998943' 
}, {
  id: 2041,
  store_id: 12,
  latitude: '40.732912',
  longitude: '-74.000083' 
}, {
  id: 2051,
  store_id: 14,
  latitude: '40.731053',
  longitude: '-74.001423' 
}, {
  id: 2061,
  store_id: 14,
  latitude: '40.729696',
    longitude: '-74.002186' 
}, {
  id: 2071,
  store_id: 14,
  latitude: '40.729121',
  longitude: '-74.002473' 
}];

const merged = myArr.reduce((merged, item) => {
  if (!merged[item.store_id]) merged[item.store_id] = [];
  merged[item.store_id].push({
    latitude: item.latitude,
    longitude: item.longitude,
  });

  return merged;
}, {});

console.log(merged)

node map and filter results into new array

1 Answers1