function pickDeep(data, keys) {
    return _.reduce(data, function(result, value, key, collection) {
        var val = null;

        if (_.isObject(value)) {
            val = pickDeep(value, keys);
        } else {
            if (keys.indexOf(key) > -1) {
                val = value;
            }
        }

        if ( (!_.isNull(val) && !_.isObject(val))
             || (_.isObject(val) && !_.isEmpty(val))) {
            if (_.isArray(result)) {
                result.push(val);
            } else {
                result[key] = val;
            }
        }

        return result;
    }, (_.isArray(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
        }
    ]
};

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