1 d3.split = function(array, f) {

     2   var arrays = [],

     3       values = [],

     4       value,

     5       i = -1,

     6       n = array.length;

     7   if (arguments.length < 2) f = d3_splitter;

     8   while (++i < n) {

     9     if (f.call(values, value = array[i], i)) {

    10       values = [];

    11     } else {

    12       if (!values.length) arrays.push(values);

    13       values.push(value);

    14     }

    15   }

    16   return arrays;

    17 };

    18 

    19 function d3_splitter(d) {

    20   return d == null;

    21 }