gistfile1.js

// map function
function(op) {
  if(op.channel) {
    emit(op.channel, op);
  }
}


// reduce
function(keys, ops, rereduce) {
  if(rereduce) {
    // still need to do this
  } else {
    var channels = {};
    ops.forEach(function(op) {
      var channel = (channels[op.channel] = channels[op.channel] || {channel: op.channel, users: []});
      if(op.operation == "join") {
        if(channel.users.indexOf(op.property) == -1) channel.users.push(op.property);
      }
    });
    return channels;
  }
}


// example operations
{
   "_id": "b3af688ce356487f5ca3176400edd87c",
   "_rev": "1-78203bea28805a6c97544b71d89ae09b",
   "operation": "join",
   "property": "mathijs",
   "channel": "couchdb"
}