Javascript: Convert Array into Object [duplicate]

Question

This question already has answers here:

Most efficient method to groupby on an array of objects (63 answers)

How can I group an array of objects by key? (32 answers)

Closed 4 years ago.

i have array:

[
 ['a', 'b', 'c'],
 ['a', 'h', 'k'],
 ['c', 'd', 'e']
]

Is there a best way to convert it on object like this?

{
 a: [
 ['a', 'b', 'c'],
 ['a', 'h', 'k'],
 ],
 c: [
 ['c', 'd', 'e']
 ]
}

• topdev87: what is the rule to convert? ask the question clearly.
• Shivansh Seth: stackoverflow.com/a/54789452/15064340 check this
• adiga: You can use any of the grouping questions like (Most efficient method to groupby on an array of objects or How to group an array of objects by key). Use '0' as the property you want to group by.
• Kiều Toàn: it is to merge all the ways elements have an equal array [0] into one key of the object

Answer 1

You can achieve it by using .reduce & Logical nullish assignment (??=)

const arrays = [
 ['a', 'b', 'c'],
 ['a', 'h', 'k'],
 ['c', 'd', 'e']
];
const result = arrays.reduce((acc, curr) => {
 const key = curr[0];
 acc[key] ??= [];
 acc[key].push(curr);
 
 return acc;
}, {})
console.log(result);

Answer 2

You can use .reduce() to get the desired output:

const data = [
 ['a', 'b', 'c'],
 ['a', 'h', 'k'],
 ['c', 'd', 'e']
];
const result = data.reduce((r, c) => {
 r[c[0]] = r[c[0]] || [];
 r[c[0]].push(c);
 return r;
}, {});
console.log(result);

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

• Nguyễn Văn Phong: You should cache the c[0] into an individual variable named key to make your code less complex as well as avoid duplication codes :) Is that ok if I edit it? sir
• Nguyễn Văn Phong: Also, you can make your code more concise like from r[c[0]] = r[c[0]] || []; to acc[key] ??= [];. Check my answer below if you like. Thanks sir :)