JavaScript array manipulation interview question [duplicate]

Question

This is a question that I have encountered during an interview:

Write a function to transform the array:

[
  {name:'a',values:[1,2]},
  {name:'b',values:[3]},
  {name:'a',values:[4,5]}
]

to:

[
  {name:'a',values:[1,2,4,5]},
  {name:'b',values:[3]}
]

I know this is not hard, but I just can't figure it out. Does anyone know how to solve it? Are there any places that I can find and practice more practical questions like this one?

Familiarize yourself with how to access and process nested objects, arrays or JSON and how to create objects and use the available static and instance methods of Object and Array. — Sebastian Simon
– Sebastian Simon, Commented Sep 17, 2021 at 10:53
You can search on LeetCode for different challenges / problems / common interview questions and practise them :) — Nakarukatoshi Uzumaki
– Nakarukatoshi Uzumaki, Commented Sep 17, 2021 at 10:53
Duplicate target found by Googling “site:stackoverflow.com js merge arrays in object by id”. — Sebastian Simon
– Sebastian Simon, Commented Sep 17, 2021 at 10:54
If you want to write the code functional, a few ideas: [...new Set(arr.map(x => x.name))].map(name => ({ name, values: arr.filter(x => x.name === name).map(x => x.values).flat() })) or Object.values(arr.reduce((a, { name, values }) => ({ ...a, [name]: { name, values: [...a[name]?.values ?? [], ...values] } }), {}))... — CherryDT
– CherryDT, Commented Sep 17, 2021 at 10:54

Ramesh Reddy · Accepted Answer · 2021-09-17 11:14:15Z

0

You can group the array by name and then get an array using the grouped object:

const bla = [
  {name:'a',values:[1,2]},
  {name:'b',values:[3]},
  {name:'a',values:[4,5]}
];

const res = Object.values(bla.reduce((obj, { name, values }) => {
  obj[name] = obj[name] ?? {name, values: []}
  obj[name].values.push(...values)
  return obj
}, {}));

console.log(res)

edited Sep 17, 2021 at 11:14

answered Sep 17, 2021 at 11:01

Ramesh Reddy

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