How to Group array of objects with same keys using javascripts?

Question

I want to make an array of objects grouped by the date property.

let data = [
        { Age: "(60-100)", Date: "28/05/20" },
        { Age: "(60-100)", Date: "28/05/20" },
        { Age: "(4-6)", Date: "28/05/20" },
        { Age: "(60-100)", Date: "29/05/20" },
        { Age: "(38-43)", Date: "29/05/20" },
        { Age: "(4-6)", Date: "29/05/20" },
        { Age: "(38-43)", Date: "30/05/20" },
        { Age: "(38-43)", Date: "30/05/20" }
    ];

I want the output like

 result = [
        { Date: "28/05/20", "(60-100)": 2, "(4-6)": 1 },
        { Date: "29/05/20", "(38-43)": 1, "(4-6)": 1, "(60-100)": 1 },
        { Date: "30/05/20", "(38-43)": 2 },
    ]

Answer 1

Try this:

function groupByDate(data){
    let groupedData = [];
    data.forEach(element => {
        //Search for the object containing the specified date
        let objIndex = groupedData.findIndex(object => {return object.Date == element.Date;})
        //If date is not created, create it
        if (objIndex == -1){
            groupedData.unshift({Date: element.Date})
            objIndex = 0;
        }
        //If age is not created, create it. Else add 1 to specified age.
        if(typeof groupedData[objIndex][element.Age] == 'undefined'){
            groupedData[objIndex][element.Age] = 1;
        } else {
            groupedData[objIndex][element.Age]++;
        }
    });
    return groupedData;
}

If you also want to sort by date, you could check out this post. Hope it helped you!