1 d3_transitionPrototype.select = function(selector) {

     2   var subgroups = [],

     3       subgroup,

     4       subnode,

     5       node;

     6 

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

     8 

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

    10     subgroups.push(subgroup = []);

    11     for (var group = this[j], i = -1, n = group.length; ++i < n;) {

    12       if ((node = group[i]) && (subnode = selector.call(node.node, node.node.__data__, i))) {

    13         if ("__data__" in node.node) subnode.__data__ = node.node.__data__;

    14         subgroup.push({node: subnode, delay: node.delay, duration: node.duration});

    15       } else {

    16         subgroup.push(null);

    17       }

    18     }

    19   }

    20 

    21   return d3_transition(subgroups, this.id, this.time).ease(this.ease());

    22 };