function (doc) {
  var ts = parseInt(doc._id);
  var date = new Date(ts);
  var y = date.getUTCFullYear();
  var m = date.getUTCMonth() + 1;
  var d = date.getUTCDate();
  var h = date.getUTCHours();
  var min = date.getUTCMinutes();
  emit([y, m, d, h, min], doc.btcinusd);
}