Group Array of objects into specific format using lodash

Question

I have this array of objects, that I need to modify to make the rendering easier . I used some code mentioned in a similar question : Group array of object nesting some of the keys with specific names

Here's my array and code

function groupAndMap(events, Year, Month, predic){
    return _.map(_.groupBy(events,Year), (obj,key) => ({
        [Year]: key,
        [Month]: (predic && predic(obj)) || obj
    }));
}

const items = [
{	
    "Year": 2018,
    "Month": 7,
    "Day": 2,
    "Title": "event1",
    "StartDate": "2018-07-02T10:00:00.000Z",
    "EndDate": "2018-07-02T11:00:00.000Z"
}, {
    "Year": 2018,
    "Month": 8,
    "Day": 31,
    "Title": "event2",
    "StartDate": "2018-07-31T10:00:00.000Z",
    "EndDate": "2018-08-02T11:00:00.000Z"
}
   
    
];

function groupAndMap(items, itemKey, childKey, predic){
    return _.map(_.groupBy(items,itemKey), (obj,key) => ({
        [itemKey]: key,
        [childKey]: (predic && predic(obj)) || obj
    }));
}

var result = groupAndMap(items,"Year","Months",
                  arr => groupAndMap(arr,"Month", "Days"));

var jsonvalue = JSON.stringify(result);
document.write(jsonvalue);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.js"></script>

I want my output to be in the following format

[{
	"Year": "2019",
	"Months": [{
		"Month": "8",
		"Days": [{
			"Day": "31",
			"Events": [{
				"Year": 2019,
				"Month": 8,
				"Day": 31,
				"Title": "event3",
				"StartDate": "2018-07-31T10:00:00.000Z",
				"EndDate": "2018-08-02T11:00:00.000Z"
			}]
		}]
	}]
}]

How should i modify the code in order to get this result ?

Nina Scholz · Accepted Answer · 2018-08-01 12:51:56Z

You could use an array with the keys to group for the nested objects.

function groupAndMap(events, groups) {
    return _(events)
        .groupBy(groups[0])
        .map((array, key) => ({
            [groups[0]]: key,
            [groups[1] + 's']: groups[2] && groupAndMap(array, groups.slice(1)) || array
        }))
        .values();          
}

var items = [{ Year: 2018, Month: 7, Day: 2, Title: "event1", StartDate: "2018-07-02T10:00:00.000Z", EndDate: "2018-07-02T11:00:00.000Z" }, { Year: 2018, Month: 8, Day: 31, Title: "event2", StartDate: "2018-07-31T10:00:00.000Z", EndDate: "2018-08-02T11:00:00.000Z" }],
    result = groupAndMap(items, ["Year", "Month", "Day", "Event"]);

console.log(result);

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

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.js"></script>

With defined keys for the result

function groupAndMap(events, groups, keys) {
    return _(events)
        .groupBy(groups[0])
        .map((array, key) => ({
            [groups[0]]: key,
            [groups[1] + 's']: groups[2] && groupAndMap(array, groups.slice(1), keys) || _.map(array, o => _.pick(o, keys))
        }))
        .values();          
}

var items = [{ Year: 2018, Month: 7, Day: 2, Title: "event1", StartDate: "2018-07-02T10:00:00.000Z", EndDate: "2018-07-02T11:00:00.000Z" }, { Year: 2018, Month: 8, Day: 31, Title: "event2", StartDate: "2018-07-31T10:00:00.000Z", EndDate: "2018-08-02T11:00:00.000Z" }],
    result = groupAndMap(items, ["Year", "Month", "Day", "Event"], ['Title', 'StartDate', 'EndDate']);

console.log(result);

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

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.js"></script>

Do you have any idea on how can i omit Year ,Month and Day keys from the Events array ? @NinaScholz

Jonas Wilms · Accepted Answer · 2018-08-01 12:08:50Z

I think its the easiest if you group by an array of criterias:

const entries = Symbol.for("entries");
const tree = { [entries]: [] };
const groups = ["Year", "Month", "Day"];
const childNames = ["Months", "Days", "Events"];

for(const item of items) {
  let node = tree;
  for(const [index, group] of groups.entries()) {
    const childName = childNames[index];
    const key = item[group];
    if(node[key]) {
      node = node[key];
    } else {
      const children = [];          
      node[entries].push({
          [group]: key,
          [childName]: children
      });
      node = node[key] = { [entries]: children };
    }
  }
  node[entries].push(item);
}

const result = tree[entries];

That allows you to access an event as:

 for(const event of tree[2017][12][31][entries])

and result contains the datastructure you needed.

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