Question

I am trying to write a function in javascript that from JSON input data returns the data belonging to a specific group, including the children of that group. The data looks like this:

            [
            {"id":"0", "name":"Person 0"},
            {"id":"1", "name":"Person 1","group":"0"},
            {"id":"2", "name":"Person 2","group":"0"},
            {"id":"3", "name":"Person 3","group":"2"},
            {"id":"4", "name":"Person 4","group":"2"},
            {"id":"5", "name":"Person 5","group":"4"},
            {"id":"6", "name":"Person 6","group":"4"},
            {"id":"7", "name":"Person 7","group":"0"},
            {"id":"8", "name":"Person 8","group":"7"}
            ]

Here, a person in group x belongs to the same group as person with id x.

For example: function(data, group) would return the following for function(data, 2):

            [
            {"id":"3", "name":"Person 3","group":"2"},
            {"id":"4", "name":"Person 4","group":"2"},
            {"id":"5", "name":"Person 5","group":"2"},
            {"id":"6", "name":"Person 6","group":"2"},
            ]

and function(data,0):

            [
            {"id":"1", "name":"Person 1","group":"1"},
            {"id":"2", "name":"Person 2","group":"2"},
            {"id":"3", "name":"Person 3","group":"2"},
            {"id":"4", "name":"Person 4","group":"2"},
            {"id":"5", "name":"Person 5","group":"2"},
            {"id":"6", "name":"Person 6","group":"2"},
            {"id":"7", "name":"Person 7","group":"7"},
            {"id":"8", "name":"Person 8","group":"7"}
            ]

I have tried to loop through the array but that doesn’t deal with the subgroups, so I guess I have to do it in a recursive fashion?

Answer 1

You can .reduce() the data array and concatenate in the sub groups.

function dataForGroup(data, group, refs) {
    if (!refs)
        refs = {};

       // check if it's in the list
    if (refs[group] === true)
        return []; // or you can throw an Error
    else
        refs[group] = true; // first encounter, so add it to the list

    return data.reduce(function(res, obj) {
        return obj.group == group ? 
                   res.concat(obj, dataForGroup(data, obj.id, refs)) : res;
    }, []);
}

Hopefully there are no circular references!

Though I don’t understand the group(data, 0) output, and I don’t see any sub-group data.