mapping JSON Data reverse?

Question

I got stuck on a maybe simple task, but could not find any solution. I have some JSON Data - lets say:

[{
  "_id": 1,
  "type": "person",
  "Name": "Hans",
  "WorksFor": ["3", "4"]
}, {
  "_id": 2,
  "type": "person",
  "Name": "Michael",
  "WorksFor": ["3"]
}, {
  "_id": 3,
  "type": "department",
  "Name": "Marketing"
}, {
  "_id": 4,
  "type": "department",
  "Name": "Sales"
}]

As I learned here it is quite simple to get all the persons and the departments they work for together using a map array for the departments. Then I can map the corresponding department to the Person and receive something like:

[{
  "_id": 1,
  "type": "person",
  "Name": "Hans",
  "WorksFor": ["3", "4"],
  "Readable": ["Marketing", "Sales"]
}, {
  "_id": 2,
  "type": "person",
  "Name": "Michael",
  "WorksFor": ["3"],
  "Readable": ["Sales"]
}]

But for another interface I need the data "the other way round" e.g.

[{
  "_id": 3,
  "type": "department",
  "Name": "Marketing",
  "employees": [
        "Hans", "Michael"
    ]
}, {
  "_id": 4,
  "type": "department",
  "Name": "Sales",
  "employees": [
        "Hans"
    ]
  }]

Is there any decent way to achieve this structure? Two days of trying didn't get me anywhere...

Answer 1

The solution using Array.prototype.filter() and Array.prototype.forEach() functions:

var data = [{ "_id": 1, "type": "person", "Name": "Hans", "WorksFor": ["3", "4"]}, { "_id": 2, "type": "person", "Name": "Michael", "WorksFor": ["3"]}, { "_id": 3, "type": "department", "Name": "Marketing"}, { "_id": 4, "type": "department", "Name": "Sales"}],
    // getting separated "lists" of departments and employees(persons) 
    deps = data.filter(function(o){ return o.type === "department"; }),
    persons = data.filter(function(o){ return o.type === "person"; });
    
deps.forEach(function (d) {
  d['employees'] = d['employees'] || [];
  persons.forEach(function (p) {
      if (p.WorksFor.indexOf(String(d._id)) !== -1) {  // check the `id` coincidence between the employee and the department
        d['employees'].push(p.Name);
      }
  });
});
    
console.log(deps);

Answer 2

You could use a hash table and a single loop for each array.

Methods:

• Array#reduce for iterating an array and returning the result,
• Array#forEach for looping the inner array WorksFor,
• Object.create(null) to generate an object without any prototypes,
• some other pattern, like a closure over hash and

• the use of logical OR || for checking a falsy value and taking an object as default.

  hash[b] = hash[b] || { _id: b, employees: [] };
  

var data = [{ _id: 1, type: "person", Name: "Hans", WorksFor: [3, 4] }, { _id: 2, type: "person", Name: "Michael", WorksFor: [3] }, { _id: 3, type: "department", Name: "Marketing" }, { _id: 4, type: "department", Name: "Sales" }],
    result = data.reduce(function (hash) {
        return function (r, a) {
            if (a.type === 'person') {
                a.WorksFor.forEach(function (b) {
                    hash[b] = hash[b] || { _id: b, employees: [] };
                    hash[b].employees.push(a.Name);
                });
            }
            if (a.type === 'department') {
                hash[a._id] = hash[a._id] || { _id: b, employees: [] };
                hash[a._id].type = a.type;
                hash[a._id].Name = a.Name;
                r.push(hash[a._id]);
            }
            return r;
        };
    }(Object.create(null)), []);

console.log(result);

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

Answer 3

You can try something like this:

var data = [{ "_id": 1, "type": "person", "Name": "Hans", "WorksFor": ["3", "4"]}, { "_id": 2, "type": "person", "Name": "Michael", "WorksFor": ["3"]}, { "_id": 3, "type": "department", "Name": "Marketing"}, { "_id": 4, "type": "department", "Name": "Sales"}]
var ignoreDept = ['person'];

var result = data.reduce(function(p,c,i,a){
  if(ignoreDept.indexOf(c.type) < 0){
    c.employees = a.reduce(function(arr,emp){
      if(emp.WorksFor && emp.WorksFor.indexOf(c._id.toString()) > -1){
        arr.push(emp.Name)
      }
      return arr;
    },[]);
    p.push(c);
  }
  return p;
}, []);

console.log(result)

Answer 4

var data = [{ "_id": 1, "type": "person", "Name": "Hans", "WorksFor": ["3", "4"]}, { "_id": 2, "type": "person", "Name": "Michael", "WorksFor": ["3"]}, { "_id": 3, "type": "department", "Name": "Marketing"}, { "_id": 4, "type": "department", "Name": "Sales"}];

var dep = {};

data.forEach(e => (e.type === 'person' && e.WorksFor.forEach(d => dep[d]? dep[d].push(e.Name): dep[d] = [e.Name])));

data.forEach(e => (e.type == 'department' && (e.employees = dep[e._id] || [])));

data = data.filter(e => e.type == 'department');

console.log(data);

Answer 5

var data = [{ "_id": 1, "type": "person", "Name": "Hans", "WorksFor": ["3", "4"] }, { "_id": 2, "type": "person", "Name": "Michael", "WorksFor": ["3"] }, { "_id": 3, "type": "department", "Name": "Marketing" }, { "_id": 4, "type": "department", "Name": "Sales" }];

var departments = [],
    persons = [];

data.forEach(e => {
  if (e.type === "person") {
    persons.push(e);
  } else if (e.type === "department") {
    departments.push(e);
    e.employees = [];
  }
});

departments.forEach(d => {
  var workers = persons.filter(p => p.WorksFor.indexOf(d._id.toString()) > -1)
                     /*.map(p => p.Name)*/    // add this if you only need the name instead of the complete "person"

  d.employees = d.employees.concat(workers);
});

console.log(JSON.stringify(departments, null, 4));

Answer 6

Here's a way you can get the first mapping. I've added some comments so you can follow along, and with it I hope you can find the answer to your second problem.

// First, let's get just the items in this array that identify persons
// I've called this array "data"
data.filter(x => x.type === 'person') 
    // Now let's map over them
    .map(person =>
      // We want all of the data associated with this person, so let's
      // use Object.assign to duplicate that data for us
      Object.assign({}, person, {
          // In addition, we want to map the ID of the WorksFor array to the Name
          // of the corresponding department. Assuming that the _id key is unique,
          // we can due this simply by mapping over the WorksFor array and finding
          // those values within the original array.
          Readable: person.WorksFor.map(wfId =>
             // Notice here the parseInt. This will not work without it due to
             // the type difference between WorksFor (string) and _id (integer)
             data.find(d => d._id === parseInt(wfId)).Name
          )
      })
);