how to merge two arrays (array 1d and array 2d object) into a array using lodash

Question

I am looking for best ways of doing this. I have two arrays (array 1d and array 2d object):

let keys = [11, 12];
let values = [
[
   { name: '1', link: '1', history: '1' },
   { name: '2', link: '2', history: '2' }
 ],
 [
   { name: '3', link: '3', history: '3' },
   { name: '4', link: '4', history: '4' }
 ]
]

The end result I want is an array of map:

[
   { name: '1', link: '1', history: '1' , q : 11},
   { name: '2', link: '2', history: '2' , q : 11},
   { name: '3', link: '3', history: '3' , q : 12},
   { name: '4', link: '4', history: '4' , q : 12}
]

How do I do it the most efficient/clean way using lodash? Thanks!

This code without lodash :

let arr = [];
let keys = [ 29, 30 ]
let values = [
  [
    { name: '1', link: '1', history: '1' },
    { name: '2', link: '2', history: '2' }
  ],
  [
    { name: '3', link: '3', history: '3' },
    { name: '4', link: '4', history: '4' }
  ]
]
for (let j = 0; j < values.length; j++) {
  for (let i = 0; i < values[j].length; i++) {
    arr.push({ ...values[j][i], q: keys[j] });
  }
}
console.log(arr)

why do you need lodash?

Nina Scholz
– Nina Scholz

2020-03-07 18:05:25 +00:00
Commented Mar 7, 2020 at 18:05 — Nina Scholz
– Nina Scholz, Commented Mar 7, 2020 at 18:05
I'm worried about the time if so much information.

sir air
– sir air

2020-03-07 18:06:31 +00:00
Commented Mar 7, 2020 at 18:06 — sir air
– sir air, Commented Mar 7, 2020 at 18:06
wait pls i think i ask wrong .

sir air
– sir air

2020-03-07 18:07:26 +00:00
Commented Mar 7, 2020 at 18:07 — sir air
– sir air, Commented Mar 7, 2020 at 18:07
@NinaScholz I edit it .

sir air
– sir air

2020-03-07 18:11:37 +00:00
Commented Mar 7, 2020 at 18:11 — sir air
– sir air, Commented Mar 7, 2020 at 18:11
How did you decide to map which keys go to which array?

bharadhwaj
– bharadhwaj

2020-03-07 18:15:10 +00:00
Commented Mar 7, 2020 at 18:15 — bharadhwaj
– bharadhwaj, Commented Mar 7, 2020 at 18:15

grodzi · Accepted Answer · 2020-03-07 19:06:52Z

2

You may simply just use _.map

let keys = [11, 12];
let values = [[{"name":"1","link":"1","history":"1"},{"name":"2","link":"2","history":"2"}],[{"name":"3","link":"3","history":"3"},{"name":"4","link":"4","history":"4"}]]
console.log(_.map(values, (v, i) => _.map(v, o => (o.q = keys[i], o))))

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.core.js"></script>

or without lodash which is pretty much the same syntax wise

let keys = [11, 12];
let values = [[{"name":"1","link":"1","history":"1"},{"name":"2","link":"2","history":"2"}],[{"name":"3","link":"3","history":"3"},{"name":"4","link":"4","history":"4"}]]
console.log(values.map((v, i) => v.map(o => (o.q = keys[i], o))))

edit: I forgot that the resulting array has to be 1D. - The lodash variation needs to get some _.flatten over the result - The native js needs a .flat()

Lastly one may use lodash/fp to get some chaining style

let keys = [11, 12];
let values = [[{"name":"1","link":"1","history":"1"},{"name":"2","link":"2","history":"2"}],[{"name":"3","link":"3","history":"3"},{"name":"4","link":"4","history":"4"}]]

console.log(
  _.flow(
    // we need to use entries to get the index of fp.map
    _.entries,
    // for each array
    _.map(([i, v]) => 
      // foreach "history" of the array
      _.map(
        // merge the key to the current "history"
        _.merge({ q: keys[i] }), v)
      ),
    _.flatten
  )(values)
)

console.log(
  _.flow(
    // or its variant
    _.map.convert({ cap: false })((v,i) => _.map(_.merge({ q: keys[i] }), v)),
    _.flatten
  )(values)
)

<script src="https://cdn.jsdelivr.net/g/lodash@4(lodash.min.js+lodash.fp.min.js"></script>

edited Mar 7, 2020 at 19:06

answered Mar 7, 2020 at 18:26

grodzi

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3 Comments

grodzi Over a year ago

I have not been precise enough but the resulting array is [[],[]], if you want a 1d array you may just use flat() at the end @sir air

sir air Over a year ago

i using _.flatMap(result) , i work for me. thanks again @grodzi

grodzi Over a year ago

you are welcome @sir air I am also adding an example using lodash/fp which people seem to like to work with (I do not share this opinion but this may be useful to you)

Nina Scholz · Accepted Answer · 2020-03-07 18:20:40Z

1

Not a lodash solution, but a universal approach for more arrays with objects for merging to get a cartesian product.

let keys = [11, 12],
    values = [[{ name: '1', link: '1', history: '1' }, { name: '2', link: '2', history: '2' }], [{ name: '3', link: '3', history: '3' }, { name: '4', link: '4', history: '4' }]],
    data = [
        values.flat(),
        keys.map(q => ({ q }))
    ],
    result = data.reduce((a, b) => a.reduce((r, v) => r.concat(b.map(w => ({ ...v, ...w }))), []));

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Mar 7, 2020 at 18:20

answered Mar 7, 2020 at 18:14

Nina Scholz

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Comments

Ori Drori · Accepted Answer · 2020-03-07 19:15:48Z

1

You can use Array.flatMap() (or lodash's _.flatMap()) to iterate the values, and then map the sub-arrays, and add the respective key:

const keys = [11, 12];
const values = [[{"name":"1","link":"1","history":"1"},{"name":"2","link":"2","history":"2"}],[{"name":"3","link":"3","history":"3"},{"name":"4","link":"4","history":"4"}]]

const result = values.flatMap((arr, i) => 
  arr.map(o => ({ ...o, q: keys[i] }))
)

console.log(result)

answered Mar 7, 2020 at 19:15

Ori Drori

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