JavaScript: Merge the elements with the same key into the array-CodePudding

I want to find duplicate elements of an array and 2 arrays of duplicate elements.

array = [
  ["41",{asd:"1"}],
  ["41",{asd:"2"}],
  ["42",{asd:"1"}],
  ["42",{asd:"2"}]
]

And the result I want

result=[
  ["41",{asd:"1"},{asd:"2"}],
  ["42",{asd:"1"},{asd:"2"}],
]

I have to use core JavaScript. Frameworks are not allowed.

CodePudding user response：

Using Array#reduce, iterate over the array while updating a Map where the key is the number and the value is its list of objects
Using Array#map, return a list of arrays with each number and its objects in one array

const array = [ ["41", {asd:"1"}], ["41", {asd:"2"}], ["42", {asd:"1"}], ["42", {asd:"2"}] ];

const res = [...
    array.reduce((map, [key, obj]) => 
      map.set(key, [...(map.get(key) || []), obj])
    , new Map)
    .entries()
  ]
  .map(([key, objArr]) => [key, ...objArr]);

console.log(res);

CodePudding user response：

reduce over the array. Extract the key and object from the array in each iteration. If the key doesn't exist on the accumulator add it and set it's value to [key], and then push the object into it. Then use Object.values to get the output you need.

const arr = [
  ["41",{asd:"1"}],
  ["41",{asd:"2"}],
  ["42",{asd:"1"}],
  ["42",{asd:"2"}]
];

const out = arr.reduce((acc, c) => {
  const [key, obj] = c;
  acc[key] = acc[key] || [key];
  acc[key].push(obj);
  return acc;
}, {});

console.log(Object.values(out));