JavaScript: How to group nested array

Question

I am trying to display data using SectionList in React Native. I have written the code below displaying what I am trying to accomplish.

I want the data to first be grouped together by date, and inside of that date, I need them grouped by location. A regular JavaScript solution will work. It's important that it has a title and data key.

My input data is in this format:

[ { game_id: 1171,
    date: '2018-11-17',
    location: 'Plaza'
   },
  { game_id: 1189,
    date: '2018-11-17',
    location: 'Field - Kickball'
   },
   { game_id: 1489,
    date: '2018-11-16',
    location: 'Field - Kickball'
   },
   { game_id: 1488,
    date: '2018-11-16',
    location: 'Field - Soccer'
   }
]

I need the obtain the following output from the data array above:

data = [{
    title: "2018-11-17",
    data: [{
            title: "Field - Kickball",
            data: [{
                game_id: 1189,
                date: '2018-11-17',
                location: 'Field - Kickball'
            }]
        },
        {
            title: "Plaza",
            data: [{
                game_id: 1171,
                date: '2018-11-17',
                location: 'Plaza'
            }]
        }
    ]
    },
    {
        title: "2018-11-16",
        data: [{
                title: "Field - Kickball",
                data: [{
                    game_id: 1489,
                    date: '2018-11-16',
                    location: 'Field - Kickball'
                }]
            },
            {
                title: "Field - Soccer",
                data: [{
                    game_id: 1488,
                    date: '2018-11-16',
                    location: 'Field - Soccer'
                }]
            }
        ]
    }
]

I have tried this already:

const games = [data here]
var groups = _(games)
.groupBy(x => x.date)
        .map(value => {
            return _.groupBy(value, 'location')
            .map(({key, value}) => ({title: key, data: value}))
        })

        .map((value, key) => {
            return ({title: value[Object.keys(value)[0]][0].date, data: value})
        })

Answer 1

There are a few ways this can be achieved, however a simple approach that does not require third party dependencies like Underscore or Lodash, can implemented with the built-in Array#reduce() method as shown below.

Please see the documentation in the following code snippet for details on how this solution works:

const input =  [ { game_id: 1171, date: '2018-11-17', location: 'Plaza' }, { game_id: 1189, date: '2018-11-17', location: 'Field - Kickball' }, { game_id: 1489, date: '2018-11-16', location: 'Field - Kickball' }, { game_id: 1488, date: '2018-11-16', location: 'Field - Soccer' } ];


/* Reduce input data to required nested sub-array structure */
const data = input.reduce((result, item) => {

  /* Construct item to be inserted into sub array for this item.date
  in resulting data object */
  const resultItem = {
    title: item.location,
    data: [{
      game_id: item.game_id,
      date: item.date,
      location: item.location
    }]
  };

  /* Find existing item in result array with title that matches date */
  const resultDateList = result.find(i => i.title === item.date);

  if (resultDateList) {

    /* If matching sublist found, add constructed item to it's data array */
    resultDateList.data.push(resultItem);
  } else {

    /* If not matching sublist found, add a new one to the result for this item
    and pre-populate the data array with new item*/
    result.push({
      title: item.date,
      data: [resultItem]
    });
  }

  return result;

}, [])

console.log(data)

Hope that helps!