How to implement MapReduce in C# using PLINQ?

Question

How to implement MapReduce in C# using PLINQ?

Suppose, you have 7-8 WebServices to collect data and on each receiving (async manner) you have to put that data into some tables of a database, in my case it is SQL Server 2008. For instance the data you are getting from each Web Service is:

 <employees>
  <employee>
   <name>Ramiz</name>
  </employee>
  <employee>
   <name>Aamir</name>
  </employee>
  <employee>
   <name>Zubair</name>
  </employee>
</employees>

And, on each receiving of response this data goes into a table name - Employee:

Employee
===
EmployeeID (PK)
EmployeeName

Once the data goes into table, it has to return as json to the client which is ASP.NET (MVC 3) application is making this call using client-side JavaScript (ajax).

Suppose, a WebServiceEmployee1 has returned with data and other 6 are in queue (still trying to get the data). Then, it should goes register the resultset into table instead of waiting other 6 and return data of inserted employee to client in json. And, keep it connected and doing while others do the same way.

Please see, in my toolbelt I have ASP.NET MVC 3 (Razor), SQL SERVER 2008 R2, jQuery.

Thanks.

Answer 1

Without clear understanding on the processing you want to perform, I suggest reading though the following MSDN documentation: http://bit.ly/Ir7Nvk It describes map/reduce with PLINQ with examples like:

public IDMultisetItemList PotentialFriendsPLinq(SubscriberID id, 
                                           int maxCandidates)
{
  var candidates = 
    subscribers[id].Friends.AsParallel()                    
    .SelectMany(friend => subscribers[friend].Friends)
    .Where(foaf => foaf != id && 
           !(subscribers[id].Friends.Contains(foaf)))
    .GroupBy(foaf => foaf)                               
    .Select(foafGroup => new IDMultisetItem(foafGroup.Key,
                                       foafGroup.Count()));
  return Multiset.MostNumerous(candidates, maxCandidates);
}

The "map" being Friends.AsParallel , SelectMany , and Where and the "reduce" phase is the GroupBy and Select

Answer 2

This PDF from MS has a Map Reduce example towards the middle/end

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0CH0QFjAE&url=http%3A%2F%2Fdownload.microsoft.com%2Fdownload%2F3%2F4%2FD%2F34D13993-2132-4E04-AE48-53D3150057BD%2FPatterns_of_Parallel_Programming_CSharp.pdf&ei=4f_VT-ScD-Lg2gWqoeSWDw&usg=AFQjCNGhk_BZL8-5n8DaS_kMTaWRU9Y1Zw&sig2=ddKl4KuOGUiUb1pIawWeNQ

public static IEnumerable<TResult> MapReduce<TSource, TMapped, TKey, TResult>(
this IEnumerable<TSource> source,
Patterns of Parallel Programming Page 76
Func<TSource, IEnumerable<TMapped>> map,
Func<TMapped, TKey> keySelector,
Func<IGrouping<TKey, TMapped>, IEnumerable<TResult>> reduce)
{
return source.SelectMany(map)
.GroupBy(keySelector)
.SelectMany(reduce);
}