Given an array of objects how do I sort the objects by a property in depth n

Question

I have an array of objects that I wish to sort by some grouping property data and a string telling me which property to group by(eg: 'Organization' or 'Organization.Name')

I need to write a function which takes in data that looks like beforeData and returns afterData

Input :

beforeData = [
{'name':'John Doe', 'Id':1, 'Organizations':[{'Id':12, 'LongName': 'Group A'},{'Id':13, 'LongName': 'Group B'}]},
{'name':'FooBar', 'Id':2, 'Organizations':[{'Id':13, 'LongName': 'Group B'},{'Id':14, 'LongName': 'Group C'}]},
{'name':'Kristine Bell', 'Id':3, 'Organizations':[{'Id':12, 'LongName': 'Group A'}]},
{'name':'Adrian P', 'Id':4, 'Organizations':[{'Id':12, 'LongName': 'Group A'}]}
]

Output:

    afterData = [
    {   
        'Group': 'Group A', 
        'entities':[
            {'name':'Adrian P', 'Id':4, 'Organizations':[{'Id':12, 'LongName': 'Group A'}]},
            {'name':'Kristine Bell', 'Id':3, 'Organizations':[{'Id':12, 'LongName': 'Group A'}]},
            {'name':'John Doe', 'Id':1, 'Organizations':[{'Id':12, 'LongName': 'Group A'},{'Id':13, 'LongName': 'Group B'}]}]
    },
    {   
        'Group': 'Group B', 
        'entities':[
            {'name':'John Doe', 'Id':1, 'Organizations':[{'Id':12, 'LongName': 'Group A'},{'Id':13, 'LongName': 'Group B'}]},
            {'name':'FooBar', 'Id':2, 'Organizations':[{'Id':13, 'LongName': 'Group B'},{'Id':13, 'LongName': 'Group C'}]},]
    },
    {   
        'Group': 'Group C', 
        'entities':[
            {'name':'FooBar', 'Id':2, 'Organizations':[{'Id':13, 'LongName': 'Group B'},{'Id':13, 'LongName': 'Group C'}]},]
    }
]

How would I go about accomplishing this? My current attempts are extremely bloated and take forever given large sets of data.

Special Kicker! : the function that solves this issue needs to be able to solve it without knowing beforehand whether the "group by property" is in depth 1 or 2(eg: 'Organization' or 'Organization.LongName').

Answer 1

Something from me:

// this function performs data extraction from an object
// the first argument is a name of the property to be extracted
// it might be just a 1st level deep value like `name`
// or nested like `foo.bar.baz`
// in case if one of intermediate items is an array - an array of
// results is returned
function dot(name, obj) {
    if (!name) {
        return obj;
    }

    var match = name.match(/^([^.]+)(?:\.(.*))?$/),
        head = match[1],
        tail = match[2];

    if (Array.isArray(obj)) {
        return obj.map(function(item) {
            return dot(name, item);
        });
    }

    if (obj === null || typeof obj != 'object') {
        return null;
    }

    return dot(tail, obj[head]);
}

// this function accepts an array of data and a key to group by
// as a result it returns an object with keys equal to a group by key
// and values that hold that key
function groupBy(data, key) {
    return data.reduce(function(result, item) {
        var keys = dot(key, item);
        if (!Array.isArray(keys)) {
            keys = [keys];
        }

        keys.forEach(function(key) {
            if (!(key in result)) {
                result[key] = [];
            }

            result[key].push(item);
        });

        return result;
    }, {});
}

console.log(groupBy(beforeData, 'Organizations.LongName'));

JSFiddle: http://jsfiddle.net/w8N4j/

It can be now easily reformatted to any other format you want.

Eg to get the exact format from the question here is a tiny transformer:

function transformerExample(hash) {
    var result = [];
    for (var key in hash) if (hash.hasOwnProperty(key)) {
        result.push({
            Group: key,
            entities: hash[key]
        });
    }

    return result;
}

PS: the main implementation obviously may not handle all possible errors. Depending on the actual requirements it is not hard to improve it.