Use Case

_.pick creates a shallow clone of an object given a predicate that identifies which keys to keep. pickDeep would perform a deep clone of the object and would "pick" up all nested objects containing the given keys. All containers containing the nested objects would remain and would not be removed.

Requirements

[Update as per comments]

• Recursively apply a pick to each level in an object.
• If a property is an object/array, then apply a pick.
• Keep all object/array only if the descendent properties fulfil the pick.

Test Cases

var testCase1 = { a: 5, b: 6};
pickDeep(testCase1, 'a'); // {a : 5}
var testCase2 = { a: 5, b: { a: 1}, c: { b: 3}};
pickDeep(testCase2, 'a'); // {a: 5, b: {a: 1}}
var testCase3 = { a: 5, b: [ { a: 1}, { c: 2}, {d: 3} ], c: [ {c: 2}, {d : 3}]}
pickDeep(testCase3, 'a'); //{ a: 5, b: [ {a: 1} ]}
var testCase4 = [ {a: 5}, {b: 2}, {c: {a :3 }}, {d: [ {a: 4}] }, z: [ { f: 34}] ];
pickDeep(testCase4, 'a'); // [ {a:5}, {c: {a:3}}, {d: [ {a:4}]}];

Improvements

I'd like any constructive criticism to improve this code, but advice I'm mainly interested in are:

• Readability
• Flexibility
• Performance

Update: changed method signature to leverage _.pick. I have a suspicion that the method signature could be improved to be more inline with functional standards in lodash/underscore.

Another idea I had, but haven't had a chance to try is performing a _.pick using the predicate that checks if the key is in keys or if the key _.isObject, then recursing on every object property.

Question

Is there a way to implement this functionality using _.cloneDeep and _.pick together?

Code jsfiddle

Function

function pickDeep(collection, identity, thisArg) {
    var picked = _.pick(collection, identity, thisArg);
    var collections = _.pick(collection, _.isObject, thisArg);

    _.each(collections, function(item, key, collection) {
        var object;
        if (_.isArray(item)) {
            object = _.reduce(item, function(result, value) {
                var picked = pickDeep(value, identity, thisArg);
                if (!_.isEmpty(picked)) {
                    result.push(picked);
                }
                return result;
            }, []);
        } else {
            object = pickDeep(item, identity, thisArg);
        }

        if (!_.isEmpty(object)) {
            picked[key] = object;
        }

    });

    return picked;
}

Test Data

var data = {
    a: 5,
    b: 6,
    c: 7,
    d: {
        a: 65,
        z: 6,
        d: {
            a: 65,
            k: 5
        }
    },
    e: [
        {a : 5},
        {b : 6},
        {c : 7}
    ],
    f: [
        { 
            b : [  { a: 5, z: 5 } ],
            c : 6
        },
        {
            g: 0   
        }
    ]
};

Execution Code

function isIn(collection) {
    return function(value, key) {
        return _.contains(collection, key);
    }
}

console.log(pickDeep(data, isIn(['a', 'c'])));