1 d3.zip = function() {

     2   if (!(n = arguments.length)) return [];

     3   for (var i = -1, m = d3.min(arguments, d3_zipLength), zips = new Array(m); ++i < m;) {

     4     for (var j = -1, n, zip = zips[i] = new Array(n); ++j < n;) {

     5       zip[j] = arguments[j][i];

     6     }

     7   }

     8   return zips;

     9 };

    10 

    11 function d3_zipLength(d) {

    12   return d.length;

    13 }