reduce function to return a sorted array of the top 50 values

top-50-by-value.js

function(doc) {
    emit(doc.parent_id, doc.visits);
}

function (keys, values, rereduce) {
  var result = [];
  var unique_keys = [];
  
  function add_to_result(parent_id, visits) {
    var index = unique_keys.indexOf(parent_id);
    if (index == -1) {
      unique_keys.push(parent_id);
      result.push({"parent_id":parent_id, "visits":visits});        
    } else {
      result[index].visits += visits;
    }
  }
  
  function sort_result(a,b) {
    if (a.visits < b.visits) return 1;
    if (a.visits > b.visits) return -1;
    return 0;
  }
  
  if (!rereduce) {
    for (var i in keys) {
      add_to_result(keys[i][0], values[i]);
    }
  }
  else {
    for each (var reduction in values) {
      for each (var item in reduction) {
        add_to_result(item.parent_id, item.visits);
      }
    }
  }
  
  return result.sort(sort_result).slice(0,50);
};