Looking to group array by values in the sub array

Question

Trying to parse one data set that has a bunch of the same "secondaryIDs" in way that i can group and iterate through them together.

In english what im trying to do is "select a unique group of all items where the value of field is unique "

'use strict';

const data = [{
    Group: 'A',
    Name: 'SD'
}, {
    Group: 'B',
    Name: 'FI'
}, {
    Group: 'A',
    Name: 'MM'
}, {
    Group: 'B',
    Name: 'CO'
}];

let unique = [...new Set(data.map(item => item.Group))];
console.log(unique);

Which gives ["A"],["B"]

but what im looking for is

{
  A: [ "SD","MM" ],
  B: [ "FI","CO" ],
}

JonnyIrving · Accepted Answer · 2018-11-13 23:13:06Z

1

For this, I would use array.reduce instead of array.map because what you're actually hoping to return is a new value, not a modified array, the reduce method is perfect when you want to literally reduce the array into a single output value, in your case an object of unique groups. Maybe try something like this:

let unique = data.reduce((acc, { Group, Name }) => {
  if (!(acc.hasOwnProperty(Group))) {
    acc[Group] = [Name];
  } else {
    acc[Group].push(Name);
  }; 
  return acc;
}, {});

I've also added a pen for this at: https://codepen.io/anon/pen/BGpgdz?editors=1011 so you can see this working.

Hope this helps!

answered Nov 13, 2018 at 23:13

JonnyIrving

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slider · Accepted Answer · 2018-11-14 01:02:18Z

1

You can also reduce your array to the grouped object (keyed by Group values):

const data = [{
  Group: 'A',
  Name: 'SD'
}, {
  Group: 'B',
  Name: 'FI'
}, {
  Group: 'A',
  Name: 'MM'
}, {
  Group: 'B',
  Name: 'CO'
}];

const grouped = data.reduce((a, {Group, Name}) => {
  if (!(Group in a)) a[Group] = [Name];
  else a[Group].push(Name);
  return a;
}, {});

console.log(grouped);

edited Nov 14, 2018 at 1:02

answered Nov 13, 2018 at 22:46

slider

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user1705722 · Accepted Answer · 2018-11-13 22:36:58Z

0

can do something like..

const map = {};
data.forEach( d => {
    if( map[d.Group] ) {
        map[d.Group].push(d.Name);
    } else {
        map[d.Group] = [d.Name];
    }
})
console.log(map)

answered Nov 13, 2018 at 22:36

user1705722

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Comments

Tom O. · Accepted Answer · 2018-11-14 00:25:57Z

0

I think the easiest way to achieve this would be to use Array.prototype.reduce method to create an object that maps unique Group names to arrays that contain Names. You can supply an empty object literal as your initial reduce accumulator:

const data = [{
  Group: 'A',
  Name: 'SD'
}, {
  Group: 'B',
  Name: 'FI'
}, {
  Group: 'A',
  Name: 'MM'
}, {
  Group: 'B',
  Name: 'CO'
}];

var namesByGroup = data.reduce((map, el) => {
  map[el.Group] ? map[el.Group].push(el.Name) : map[el.Group] = [el.Name];
  return map;
}, {});

console.log(namesByGroup);

answered Nov 14, 2018 at 0:25

Tom O.

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Comments

customcommander · Accepted Answer · 2018-11-14 00:38:56Z

0

If you're interested in a functional approach, here is a solution using Ramda:

const group =
  R.pipe(
    R.groupBy(R.prop('Group')),
    R.map(R.map(R.prop('Name'))));

console.log(
  group([
    {Group: 'A', Name: 'SD'},
    {Group: 'B', Name: 'FI'},
    {Group: 'A', Name: 'MM'},
    {Group: 'B', Name: 'CO'}])
);

<script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.min.js"></script>

answered Nov 14, 2018 at 0:38

customcommander

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Comments

Varun Suresh Kumar · Accepted Answer · 2019-02-19 13:18:51Z

0

can also be done using forEach

const data = [{
	Group: 'A',
	Name: 'SD'
}, {
	Group: 'B',
	Name: 'FI'
}, {
	Group: 'A',
	Name: 'MM'
}, {
	Group: 'B',
	Name: 'CO'
}];

const somefunction = (data) => {
let arr = {}
data.forEach( ({Group, Name}) => {
  Group in arr ?  arr[Group].push(Name) : arr[Group] = [Name]
})
return arr;
}

console.log(somefunction(data))

answered Feb 19, 2019 at 13:18

Varun Suresh Kumar

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