gistfile1.js

function (key, values, rereduce) {
        // value -> [count, min, max, mean]
        var i = 0
          , l = values.length
          , min = values[i][2] // set min to the first max
          , max = 0
          , weighted_sum_of_means = 0
          , count = 0
          , cur_count // just for clarity, feel free to remove later
          , cur_min
          , cur_max
          , cur_mean
          ;
        
        for (; i < l; i++) {
          cur_count = values[i][0];
          cur_min = values[i][1];
          cur_max = values[i][2];
          cur_mean = values[i][3];
          count = count + cur_count;
          min = Math.min(min, cur_min);
          max = Math.max(max, cur_max);
          weighted_sum_of_means = weighted_sum_of_means + (cur_count * cur_mean);
        }
        
        return [count, min, max, weighted_sum_of_means / count];
    }