Filter array of objects by another array with duplicate keys

Question

I have this array of objects:

const data = [
    {
       id: 1,
       name: 'Name1',
       encryptionKey: 'AAA'
    },
    {
       id: 2,
       name: 'Name2',
       encryptionKey: 'BBB'
    },
    {
       id: 3,
       name: 'Name3',
       encryptionKey: 'CCC'
    }
 ]

and another array of encryption keys:

const encryptionKeys = ['AAA', 'BBB']

I am then filtering the data array based on the encryptionKeys array like this:

var filtered = data.filter(function(item) {
   return encryptionKeys.indexOf(item.encryptionKey) !== -1;
});

which works and filters the objects and saves them in a new array. The problem is however if the encryptionKey array has duplicated keys, for example:

const encryptionKeys = ['AAA', 'BBB', 'BBB']

then all duplicate keys will be ignored and the filtered array will only have, in this case, 2 objects instead of 3. What am I doing wrong in my filtering code? The filtered array should have duplicate objects if the encryptionKeys array has duplicate values.

do you have items in encryptionKeys which are not in data? — Nina Scholz
– Nina Scholz, Commented Mar 29, 2019 at 9:35
So if BBB exists n times then you want the Objects with the encryptionKey BBB to appear in the filtered result n times? — Francis Leigh
– Francis Leigh, Commented Mar 29, 2019 at 10:02

Francis Leigh · Accepted Answer · 2019-03-29 10:36:00Z

1

Make note of .flat() 's Browser compatibility and then see @babel/polyfill

const data = [
  {
    id: 1,
    name: 'Name1',
    encryptionKey: 'AAA'
  },
  {
    id: 2,
    name: 'Name2',
    encryptionKey: 'BBB'
  },
  {
    id: 3,
    name: 'Name3',
    encryptionKey: 'CCC'
  }
]
const keys = ['AAA', 'BBB', 'BBB', 'AAA', 'BBB', 'ZZZ']

const occurances = data.map(d => {
  const { encryptionKey } = d
  const keyedOccurances = keys
                        .filter(k => k === encryptionKey)
                        .map(k => encryptionKey === k && d)

  return keyedOccurances.length && keyedOccurances
})
.filter(Boolean)
.flat()

console.log(occurances)

edited Mar 29, 2019 at 10:36

answered Mar 29, 2019 at 10:13

Francis Leigh

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Comments

Jack Bashford · Accepted Answer · 2019-03-29 09:35:59Z

1

Easy - just use filter on encryptionKeys beforehand:

var filtered = data.filter(function(item) {
   return encryptionKeys.filter((e, i, a) => a.indexOf(e) == i).indexOf(item.encryptionKey) !== -1;
});

Alternatively, make an Array from a Set:

var filtered = data.filter(function(item) {
   return [...new Set(encryptionKeys)].indexOf(item.encryptionKey) !== -1;
});

answered Mar 29, 2019 at 9:35

Jack Bashford

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1 Comment

Kos Cos Over a year ago

I tried your solutions but the filtered array still has only 2 objects instead of 3.

Avanthika · Accepted Answer · 2019-03-29 09:37:20Z

0

Make your encryption keys unique before you compare and filter it.

var encryptionKeys = ['AAA', 'BBB', 'BBB'];
var unique = encryptionKeys.filter((v, i, a) => a.indexOf(v) === i); 
console.log(unique);

answered Mar 29, 2019 at 9:37

Avanthika

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Comments

Nina Scholz · Accepted Answer · 2019-03-29 09:42:49Z

You could map the wanted items.

const
    data = [{ id: 1, name: 'Name1', encryptionKey: 'AAA' }, { id: 2, name: 'Name2', encryptionKey: 'BBB' }, { id: 3, name: 'Name3', encryptionKey: 'CCC' }],
    encryptionKeys = ['AAA', 'BBB', 'BBB'],
    result = encryptionKeys.map(key => data.find(o => o.encryptionKey === key));
     
console.log(result);

A short approach with a Map and filtering the keys in advance.

const
    data = [{ id: 1, name: 'Name1', encryptionKey: 'AAA' }, { id: 2, name: 'Name2', encryptionKey: 'BBB' }, { id: 3, name: 'Name3', encryptionKey: 'CCC' }],
    encryptionKeys = ['AAA', 'BBB', 'BBB', 'DDD'],
    map = new Map(data.map(o => [o.encryptionKey, o])),
    result = encryptionKeys
        .filter(Map.prototype.has, map)
        .map(Map.prototype.get, map);
     
console.log(result);

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