如何在JavaScript中将两个依赖的数组减少为一个对象？

Question

I have two JavaScript arrays of strings as a result from a SQL query (each array is one column in a result) which may contain duplicities like:

arrOne = ["key_1", "key_1", "key_2", "key_3", "key_1", "key_1"]
arrTwo = ["val_1", "val_1", "val_3", "val_3", "val_2", "val_3"]

and I need to reduce them into an object like:

newObj = {
  key_1: ["val_1", "val_2", "val_3"],
  key_2: ["val_3"],
  key_3: ["val_3"]
}

So basically, for each key, value pair, the value should be a reduced list of unique values from an arrTwo.

I have tried:

let newObj = arrOne.reduce((o, k, i) => ({...o, [k]: arrTwo[i]}), {})

which gives me:

{ key_1: 'val_3', key_2: 'val_3', key_3: 'val_3' }

but I need arrTwo[i] part to be reduced list of values instead of last value for each key.

This may have an elegant one-line solution but I am new in JavaScript and I can't find the proper solution (I think a loop is not necessary here).

Answer 1

You could take a Set and collect all values.

 var arrOne = ["key_1", "key_1", "key_2", "key_3", "key_1", "key_1"], arrTwo = ["val_1", "val_1", "val_3", "val_3", "val_2", "val_3"], newObj = arrOne.reduce( (o, k, i) => ({ ...o, [k]: [...new Set([...(o[k] || []), arrTwo[i]])] }), {} ); console.log(newObj); 

Answer 2

Use reduce on one of the first array and use index to access property from second array

 var arrOne = ["key_1", "key_1", "key_2", "key_3", "key_1", "key_1"] var arrTwo = ["val_1", "val_1", "val_3", "val_3", "val_2", "val_3"] let newObj = arrOne.reduce(function(acc, curr, index) { // check if the object has such key and if it dont contain the corresponding value if (acc[curr] && acc[curr].indexOf(arrTwo[index]) === -1) { acc[curr].push(arrTwo[index]) } else { acc[curr] = []; acc[curr].push(arrTwo[index]) } return acc; }, {}); console.log(newObj) 

Answer 3

 const arrOne = ["key_1", "key_1", "key_2", "key_3", "key_1", "key_1"]; const arrTwo = ["val_1", "val_1", "val_3", "val_3", "val_2", "val_3"]; console.log( arrTwo.reduce((a, c, i) => { if (a[arrOne[i]].indexOf(c) == -1) a[arrOne[i]].push(c); return a; }, arrOne.reduce((a, c) => { a[c] = []; return a; }, {})));