d3.split = function(array, f) {

  var arrays = [],

      values = [],

      value,

      i = -1,

      n = array.length;

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

  while (++i < n) {

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

      values = [];

    } else {

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

      values.push(value);

    }

  }

  return arrays;

};

function d3_splitter(d) {

  return d == null;

}