code: function jenksBreaks(data, lower_class_limits, n_classes) {
  
          var k = data.length - 1,
              kclass = [],
              countNum = n_classes;
  
          // the calculation of classes will never include the upper and
          // lower bounds, so we need to explicitly set them
          kclass[n_classes] = data[data.length - 1];
          kclass[0] = data[0];
  
          // the lower_class_limits matrix is used as indices into itself
          // here: the `k` variable is reused in each iteration.
          while (countNum > 1) {
              kclass[countNum - 1] = data[lower_class_limits[k][countNum] - 2];
              k = lower_class_limits[k][countNum] - 1;
              countNum--;
          }
  
          return kclass;
      }
docs: ## Pull Breaks Values for Jenks  the second part of the jenks recipe: take the calculated matrices and derive an array of n breaks.