Node.js javascript: Reduce Array of Object by Multiple Key Value

I have the following array of objects in a Node.js script:

[ 
{ 
    start: '10-05-2018',    
    assigned_agent: '1257434'
     },
  { 
    start: '10-05-2018',
    assigned_agent: '1257434'
    },
  { 
    start: '10-05-2018',
    assigned_agent: '1257434'
   },
  { 
    start: '10-06-2018',    
    assigned_agent: '1257434'
    },
  { 
    start: '10-05-2018',   
    assigned_agent: '1277852'
     },
  { 
    start: '10-05-2018',
    assigned_agent: '1277852'
  }
 ]

What I need is to have this grouped by the start and assigned_agent keys. I have tried filter function examples but no luck. Not, there are other key/value pairs in the array but omitting them for the sake of clarity. Also, while this is a Node.js script I do have Lodash available if that helps.

Thank you.

Answer

If you are ok with using lodash, try groupBy

const data = [
  { start: "10-05-2018", assigned_agent: "1257434" },
  { start: "10-05-2018", assigned_agent: "1257434" },
  { start: "10-05-2018", assigned_agent: "1257434" },
  { start: "10-06-2018", assigned_agent: "1257434" },
  { start: "10-05-2018", assigned_agent: "1277852" },
  { start: "10-05-2018", assigned_agent: "1277852" },
]

const group_by_both = _.chain(data)
  .groupBy((el) => `${el.start} ${el.assigned_agent}`)
  .values()
  .value()

console.log(group_by_both)

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

<script src="https://cdn.jsdelivr.net/npm/lodash@4.17.20/lodash.min.js"></script>