Unable to get the desired result array

Question

I am currently learning lodash and moment.js and I'm using some dummy data.The dummy data that contains a list of 1000 doctors.I have started working with Array.prototype.map() and Array.prototype.filter() and will be converting them to lodash soon.

data

var doctors = [
  {
    "id": 0,
    "dateOfEmployment": "2012-12-27",
    "dateOfTermination": "2015-01-13",
    "dateOfBirth": "1978-06-06",
    "gender": "Male"
  },
  {
    "id": 1,
    "dateOfEmployment": "2016-02-08",
    "dateOfTermination": null,
    "dateOfBirth": "1984-04-21",
    "gender": "Female"
  },
  {
    "id": 2,
    "dateOfEmployment": "2010-11-30",
    "dateOfTermination": "2015-09-03",
    "dateOfBirth": "1975-09-24",
    "gender": "Male"
  },
  {
    "id": 3,
    "dateOfEmployment": "2012-06-17",
    "dateOfTermination": null,
    "dateOfBirth": "1980-08-31",
    "gender": "Female"
  },..];

I would like to get a result of array for the last 2 years:

[{ date: '2015-04', count: 22 }, 
 { date: '2015-05', count: 25 },
 ...]

Initially I tried this:

    doctors = doctors.filter(function(doctor){
             return moment(doctor.dateOfEmployment).isBetween('2014-04', '2016-04');   
          }).map(function(doctor){
              return  {
            dates: moment(doctor.dateOfEmployment).format('YYYY-MM'),
            count: new Date(doctor.dateOfEmployment) - new Date(doctor.dateOfEmployment) + 1 };
      }););


console.log(doctors);

I am confused. Should I first create a new array of doctors with just id, dateOfEmployment, dateOfTermination and momentize both dates. Then filter the new date array with a condition where moment isBetween the years and then map/reduce.

I did think of brute-force method where I would loop through 24 times on each doctor and increment a counter based on the condition that if doctorsEmployment date and doctorsTermination date is either null or equal to the temporary date.The temporary date starting from '2014-04' to '2016-04' and finally pushing it to array the result object.

Am I approaching this problem in a wrong way?

Any help will be greatly appreciated!

Answer 1

Not lodash or moment.js, but here's how to do it in plain JS:

// Sample data
var doctors = [
  {
    "id": 0,
    "dateOfEmployment": "2012-12-27",
    "dateOfTermination": "2015-01-13",
    "dateOfBirth": "1978-06-06",
    "gender": "Male"
  },
  {
    "id": 1,
    "dateOfEmployment": "2016-02-08",
    "dateOfTermination": null,
    "dateOfBirth": "1984-04-21",
    "gender": "Female"
  },
  {
    "id": 2,
    "dateOfEmployment": "2016-02-29",
    "dateOfTermination": "2015-09-03",
    "dateOfBirth": "1975-09-24",
    "gender": "Male"
  },
  {
    "id": 3,
    "dateOfEmployment": "2015-06-17",
    "dateOfTermination": null,
    "dateOfBirth": "1980-08-31",
    "gender": "Female"
  }];
 
// Parse ISO date string (e.g. 2016-04-01) as local
function parseISODate(s) {
  var b = s.split(/\D/);
  return new Date(b[0], b[1]? b[1] - 1 : 0, b[2] || 1);
}

var startDate = parseISODate('2014-04'),
    endDate   = parseISODate('2016-04');

// Creates an object with months and counts
var resultObj = doctors.reduce(function(acc, cur) {
  var d = parseISODate(cur.dateOfEmployment);
  if (d >= startDate && d <= endDate) {
    var month = d.toISOString().slice(0,7);
    acc[month] = (acc[month] || 0) + 1;
  }
  return acc;
}, {});

// Creates an array with required objects from result object
var resultArr = Object.keys(resultObj).map(function(key) {
  return {date: key, count: resultObj[key]};
})
 
document.write(
  JSON.stringify(resultObj) + '<br>' + // {"2016-02":2,"2015-06":1}
  JSON.stringify(resultArr)  // [{"date":"2016-02","count":2},{"date":"2015-06","count":1}]
);

This assumes you only want months that have a count greater than zero. It goes through the original data once, then the result object once, though I can't see how the array is a more desirable format than the object it's created from.

Note that I edited the source data to have two dateOfEmployment dates in February, 2016.