Convert array into shorter array

Question

I have array object -

[
 { 
  department:"Reviewer",
  name:"John"
 },
 { 
  department:"Reviewer",
  name:"Carol"
 },
 { 
  department:"Reviewer",
  name:"June"
 },
 { 
  department:"Assistant Reviewer",
  name:"Mac"
 },
 { 
  department:"Assistant Reviewer",
  name:"Issac"
 }
]

I want to convert this object into array object as below -

[
     { 
      department:"Reviewer",
      name:"John;Carol;June;"
     },
     { 
      department:"Assistant Reviewer",
      name:"Mac;Issac;"
     },
]

I tried using filter -

[... new Set(obj.department)].map((item)=>{return {item.name+";"} });

But this operation is dealing with only one element per item. Its not accumulating names.

Possible duplicate of [How to group by and sum an array of objects?](https://stackoverflow.com/questions/29364262) and [Group by similar attribute and join them by comma javascript - Mysql group concat like](https://stackoverflow.com/questions/50148383) — adiga, Feb 03 '23 at 06:23
@Unmitigated it's the exact same operators. Use `+` operator on strings instead of numbers. This is probably a better target: [Group by similar attribute and join them by comma javascript - Mysql group concat like](https://stackoverflow.com/questions/50148383) — adiga, Feb 03 '23 at 06:26

Andrew Parks · Accepted Answer · 2023-02-03T07:16:59.910

Get a set of distinct departments, then map from them to the list of names

const data = [{"department":"Reviewer","name":"John"},{"department":"Reviewer","name":"Carol"},{"department":"Reviewer","name":"June"},{"department":"Assistant Reviewer","name":"Mac"},{"department":"Assistant Reviewer","name":"Issac"}]

console.log([...new Set(data.map(i=>i.department))].map(i=>({
  department: i, 
  name: data.filter(j=>j.department===i).map(j=>j.name).join(';')+';'})))

or, using reduce:

const data = [{"department":"Reviewer","name":"John"},{"department":"Reviewer","name":"Carol"},{"department":"Reviewer","name":"June"},{"department":"Assistant Reviewer","name":"Mac"},{"department":"Assistant Reviewer","name":"Issac"}]

console.log(Object.values(data.reduce((a,{department, name})=>
  (((a[department]??={department,name:''}).name+=`${name};`),a),{})))

score 1 · Answer 2 · answered Feb 03 '23 at 06:41

This would also work:

const input = [ { department: "Reviewer", name: "John", }, { department: "Reviewer", name: "Carol", }, { department: "Reviewer", name: "June", }, { department: "Assistant Reviewer", name: "Mac", }, { department: "Assistant Reviewer", name: "Issac", }, ];

const output = input.reduce((prev, { department, name }) => {
  const match = prev.find((item) => item.department === department);
  if (match) {
    match.name = `${match.name};${name}`;
  } else {
    prev.push({ department, name });
  }
  return prev;
}, []);

console.log(output);

Using Array.prototype.reduce() and Array.prototype.find()

score 1 · Answer 3 · answered Feb 03 '23 at 07:10

Here is a solution using:

.reduce() to build an object that maps from department (aka key) to names (aka value)
.map() to transform that object into an array of objects with desired format

Note that this solution is faster than an array index search (aka other answers here) for large a large input array, at the cost of using a bit more memory.

const array = [
  { department: "Reviewer", name: "John" },
  { department: "Reviewer", name: "Carol" },
  { department: "Reviewer", name: "June" },
  { department: "Assistant Reviewer", name: "Mac" },
  { department: "Assistant Reviewer", name: "Issac" }
];

const result = Object.entries(array.reduce((acc, obj) => {
  if(acc[obj.department]) {
    acc[obj.department] += obj.name + ';';
  } else {
    acc[obj.department] = obj.name + ';';
  }
  return acc;
}, {})).map(arr => ({ department: arr[0], name: arr[1] }));

console.log(result);

Jordy · Answer 4 · 2023-02-03T07:27:51.013

This codes should work:

let data = [
  { department: "Reviewer", name: "John" },
  { department: "Reviewer", name: "Carol" },
  { department: "Reviewer", name: "June" },
  { department: "Assistant Reviewer", name: "Mac" },
  { department: "Assistant Reviewer", name: "Issac" }
];

let newData = [];
data.forEach((obj)=>{
  if(newData.filter(m => m.department == obj.department).length) {
    newData.find(n => n.department == obj.department).name += obj.name + ';'; 
  } else {
    newData.push({
      department: obj.department,
      name: obj.name + ';'
    })
  } 
});
console.log(newData);

Convert array into shorter array

4 Answers4