如何将数组转换为对象？

Question

What is the best way to transform an array like this:

const arr = [
  { name: 'Bob' },
  { name: 'Ben' }
  { name: 'Cole' }
  { name: 'Mary' }
  { name: 'Travis' }
]

to an object like:

const obj = {
  'B': ['Bob', 'Ben'],
  'C': ['Cole'],
  'M': ['Mary'],
  'T': ['Travis']
}

Using only vanilla JS

Answer 1

You can use array#reduce . Iterate through each object of your array and then extract out the first letter and add names corresponding to it.

 const arr = [{name: 'Bob'}, {name: 'Ben'}, {name: 'Cole'}, {name: 'Mary'}, {name: 'Travis'}], result = arr.reduce((r,{name}) => { r[name[0]] = r[name[0]] || []; r[name[0]].push(name); return r; },{}); console.log(result);

Answer 2

Vanilla JS you say? Here you go

 let nil = x => x === undefined; let empty = ([h]) => nil(h); let first = ([h]) => h; let last = ([h, ...t]) => empty(t) ? h : last(t); let map = ([h, ...t], f) => nil(h) ? [] : [f(h), ...map(t, f)]; let reduce = ([h, ...t], f, i) => nil(h) ? i : reduce(t, f, f(i, h)); let tab = (a, f) => map(a, x => [x, f(x)]); let push = (a, x) => nil(a) ? [x] : [...a, x]; let groupBy = (a, f) => _groupBy(tab(a, f)); let _groupBy = ka => reduce(ka, (g, [x, k]) => ({...g, [k]: push(g[k], x)}), {}); /// const arr = [{ name: 'Bob' },{ name: 'Ben' },{ name: 'Cole' },{ name: 'Mary' },{ name: 'Travis' }] z = groupBy(map(arr, x => x.name), first) console.log(z)

No built-ins!

Answer 3

I created an array where the key is the first letter of the name using the reduce function and restructuring the 'name' from the objects. If the key exists in the array the name is pushed (using spread operator). Else, it creates the key with only one element.

const arr = [
  { name: 'Bob' },
  { name: 'Ben' },
  { name: 'Cole' },
  { name: 'Mary' },
  { name: 'Travis' }
];

const obj = arr.reduce((res, {name})=>{
  res[name[0]] = res[name[0]] ? [...res[name[0]],name] : [name];
  return res;
}, {});

console.log(obj);

Answer 4

let obj = {};
arr.forEach( e => {
  const name = e.name;
  if (!obj[name.charAt(0)]) obj[name.charAt(0)] = [];
  obj[name.charAt(0)].push(name);
})

I'm generating a new object and adding to it news keys based in the first char of the name values (only if the key hasn't been already added). Then, I add each value to the key that corresponds.

Answer 5

I think this thread is missing a non functional answer, so here it is:

const obj = {};

for(const {name} of arr)
  (obj[name[0]] || (obj[name[0]] = [])).push({name});