1 d3_selectionPrototype.select = function(selector) {

     2   var subgroups = [],

     3       subgroup,

     4       subnode,

     5       group,

     6       node;

     7 

     8   if (typeof selector !== "function") selector = d3_selection_selector(selector);

     9 

    10   for (var j = -1, m = this.length; ++j < m;) {

    11     subgroups.push(subgroup = []);

    12     subgroup.parentNode = (group = this[j]).parentNode;

    13     for (var i = -1, n = group.length; ++i < n;) {

    14       if (node = group[i]) {

    15         subgroup.push(subnode = selector.call(node, node.__data__, i));

    16         if (subnode && "__data__" in node) subnode.__data__ = node.__data__;

    17       } else {

    18         subgroup.push(null);

    19       }

    20     }

    21   }

    22 

    23   return d3_selection(subgroups);

    24 };

    25 

    26 function d3_selection_selector(selector) {

    27   return function() {

    28     return d3_select(selector, this);

    29   };

    30 }