How to iterate through an array of object properties, in an array of objects

Question

I have an array of objects, that looks like this:

data = [
  {
    title: 'John Doe',
    departments: [
      { name: 'Marketing', slug: 'marketing'},
      { name: 'Sales', slug: 'sales'},
      { name: 'Administration', slug: 'administration'},
    ]
  },
  {
    title: 'John Doe Junior',
    departments: [
      { name: 'Operations', slug: 'operations'},
      { name: 'Sales', slug: 'sales'},
    ]
  },
  {
    title: 'Rick Stone',
    departments: [
      { name: 'Operations', slug: 'operations'},
      { name: 'Marketing', slug: 'marketin'},
    ]
  },
]

How can I iterate over each object's departments array and create new arrays where I would have employees sorted by departments, so that the end result would like this:

operations = [
  {
    title: 'John Doe Junior',
    departments: [
      { name: 'Operations', slug: 'operations'},
      { name: 'Sales', slug: 'sales'},
    ]
  },
  {
    title: 'Rick Stone',
    departments: [
      { name: 'Operations', slug: 'operations'},
      { name: 'Marketing', slug: 'marketin'},
    ]
  },
]

marketing = [
  {
    title: 'John Doe',
    departments: [
      { name: 'Marketing', slug: 'marketing'},
      { name: 'Sales', slug: 'sales'},
      { name: 'Administration', slug: 'administration'},
    ]
  },
  {
    title: 'Rick Stone',
    departments: [
      { name: 'Operations', slug: 'operations'},
      { name: 'Marketing', slug: 'marketin'},
    ]
  },
]

What would be the way to create dynamically this kind of arrays?

Update

I have tried to come up with a solution using the suggestion from the answer, where I would dynamically create an array with department objects that would have an array of employees:

const isInDepartment = departmentToCheck => employer => employer.departments.find(department => department.slug == departmentToCheck);

var departments = [];
function check(departments, name) {
  return departments.some(object => name === object.department);
}

employees.forEach((employee) => {
    employee.departments.forEach((department) => {
        let found = check(departments, department.slug);
        if (!found) { 
            departments.push({ department: department.slug }); 
        }
        });
});

departments.forEach((department) => {
    // push an array of employees to each department
    //employees.filter(isInDepartment(department));
});

But, I don't know how can I push the array of employees to the object in the array that I am looping at the end? This is the fiddle.

Answer 1

How about this? I use Array.protoype.filter operation, and I use a higher-order function (in this case a function that returns a function) to create the predicate (function that returns a boolean) that will check whether an employee is in a specific department. I added some (hopefully) clarifying comments in the code.

Edit: with the new code and context you provided this JSFiddle demo shows how it would work together.

const employees = [
  {
    title: 'John Doe',
    departments: [
      { name: 'Marketing', slug: 'marketing'},
      { name: 'Sales', slug: 'sales'},
      { name: 'Administration', slug: 'administration'}
    ]
  },
  {
    title: 'John Doe Junior',
    departments: [
      { name: 'Operations', slug: 'operations'},
      { name: 'Sales', slug: 'sales'}
    ]
  },
  {
    title: 'Rick Stone',
    departments: [
      { name: 'Operations', slug: 'operations'},
      { name: 'Marketing', slug: 'marketin'}
    ]
  }
];

// given a department, this returns a function that checks
// whether an employee is in the specified department
// NOTE: the "find" returns the found object (truthy) 
// or undefined (falsy) if no match was found.
const isInDepartment = 
 departmentToCheck =>
     employee => employee.departments.find(dep => dep.name == departmentToCheck);

const employeesInMarketing = employees.filter(isInDepartment('Marketing'));
const employeesInOperations = employees.filter(isInDepartment('Operations'));

console.log('Employees in marketing', employeesInMarketing);
console.log('Employees in operations', employeesInOperations);