I have an array of lines:

   this.lines = [
    0: {indexLine: 0, group: 16, columns: [,…]}
    1: {indexLine: 1, group: 16,…}
    2: {indexLine: 2, group: 16,…}
    3: {indexLine: 3, group: 9,…}
    ]

I want to group lines by group to be able render it in different tables.

I have tried this:

 let arr: any = {};
        this.lines.forEach((line) => {
          if (!arr[line.group]) {
            arr[line.group] = [];
          }

          arr[line.group].push(line);
        });

>Solution :

You can use Set to get unique group values from array of object. new Set(lines.map(x => x.group) will give you array of unique values of group.

Convert that set to array with Array.from().

Now you can use map to iterate through unique group values and Array.filter would give you all matching elements.

let lines = [
    {indexLine: 0, group: 16},
    {indexLine: 1, group: 16},
    {indexLine: 2, group: 16},
    {indexLine: 3, group: 9},
];

const groupedLines = Array.from(new Set(lines.map(x=>x.group))).map(y => lines.filter(z => z.group === y));

console.log(groupedLines);