Map and Reduce in NET

Question

What scenarios would warrant the use of the  Map and Reduce  algorithm    Is there a  NET implementation of this algorithm

User · Answer

Since I never can remember that LINQ calls it Where, Select and Aggregate instead of Filter, Map and Reduce so I created a few extension methods you can use:

IEnumerable<string> myStrings = new List<string>() { "1", "2", "3", "4", "5" };
IEnumerable<int> convertedToInts = myStrings.Map(s => int.Parse(s));
IEnumerable<int> filteredInts = convertedToInts.Filter(i => i <= 3); // Keep 1,2,3
int sumOfAllInts = filteredInts.Reduce((sum, i) => sum + i); // Sum up all ints
Assert.Equal(6, sumOfAllInts); // 1+2+3 is 6

Here are the 3 methods (from https://github.com/cs-util-com/cscore/blob/master/CsCore/PlainNetClassLib/src/Plugins/CsCore/com/csutil/collections/IEnumerableExtensions.cs ):

public static IEnumerable<R> Map<T, R>(this IEnumerable<T> self, Func<T, R> selector) {
    return self.Select(selector);
}

public static T Reduce<T>(this IEnumerable<T> self, Func<T, T, T> func) {
    return self.Aggregate(func);
}

public static IEnumerable<T> Filter<T>(this IEnumerable<T> self, Func<T, bool> predicate) {
    return self.Where(predicate);
}

Some more details from https://github.com/cs-util-com/cscore#ienumerable-extensions :

User · Answer

Since I never can remember that LINQ calls it Where, Select and Aggregate instead of Filter, Map and Reduce so I created a few extension methods you can use:

IEnumerable<string> myStrings = new List<string>() { "1", "2", "3", "4", "5" };
IEnumerable<int> convertedToInts = myStrings.Map(s => int.Parse(s));
IEnumerable<int> filteredInts = convertedToInts.Filter(i => i <= 3); // Keep 1,2,3
int sumOfAllInts = filteredInts.Reduce((sum, i) => sum + i); // Sum up all ints
Assert.Equal(6, sumOfAllInts); // 1+2+3 is 6

Here are the 3 methods (from https://github.com/cs-util-com/cscore/blob/master/CsCore/PlainNetClassLib/src/Plugins/CsCore/com/csutil/collections/IEnumerableExtensions.cs ):

public static IEnumerable<R> Map<T, R>(this IEnumerable<T> self, Func<T, R> selector) {
    return self.Select(selector);
}

public static T Reduce<T>(this IEnumerable<T> self, Func<T, T, T> func) {
    return self.Aggregate(func);
}

public static IEnumerable<T> Filter<T>(this IEnumerable<T> self, Func<T, bool> predicate) {
    return self.Where(predicate);
}

Some more details from https://github.com/cs-util-com/cscore#ienumerable-extensions :

User · Answer

Linq equivalents of Map and Reduce   If you   re lucky enough to have linq then you don   t need to write your own map and reduce functions  C  3 5 and Linq already has it albeit under different names    Map is Select   Enumerable Range 1  10  Select x   gt  x   2    Reduce is Aggregate   Enumerable Range 1  10  Aggregate 0   acc  x    gt  acc   x    Filter is Where   Enumerable Range 1  10  Where x   gt  x   2    0      https   www justinshield com 2011 06 mapreduce-in-c

User · Answer

The classes of problem that are well suited for a mapreduce style solution are problems of aggregation   Of extracting data from a dataset   In C   one could take advantage of LINQ to program in this style   From the following article  http   codecube net 2009 02 mapreduce-in-c-using-linq      the GroupBy method is acting as the map  while the Select method does the job of reducing the intermediate results into the final list of results    var wordOccurrences   words                  GroupBy w   gt  w                   Select intermediate   gt  new                                       Word   intermediate Key                      Frequency   intermediate Sum w   gt  1                                      Where w   gt  w Frequency  gt  10                   OrderBy w   gt  w Frequency     For the distributed portion  you could check out DryadLINQ  http   research microsoft com en-us projects dryadlinq default aspx

User · Answer

Linq equivalents of Map and Reduce   If you   re lucky enough to have linq then you don   t need to write your own map and reduce functions  C  3 5 and Linq already has it albeit under different names    Map is Select   Enumerable Range 1  10  Select x   gt  x   2    Reduce is Aggregate   Enumerable Range 1  10  Aggregate 0   acc  x    gt  acc   x    Filter is Where   Enumerable Range 1  10  Where x   gt  x   2    0      https   www justinshield com 2011 06 mapreduce-in-c

User · Answer

The classes of problem that are well suited for a mapreduce style solution are problems of aggregation   Of extracting data from a dataset   In C   one could take advantage of LINQ to program in this style   From the following article  http   codecube net 2009 02 mapreduce-in-c-using-linq      the GroupBy method is acting as the map  while the Select method does the job of reducing the intermediate results into the final list of results    var wordOccurrences   words                  GroupBy w   gt  w                   Select intermediate   gt  new                                       Word   intermediate Key                      Frequency   intermediate Sum w   gt  1                                      Where w   gt  w Frequency  gt  10                   OrderBy w   gt  w Frequency     For the distributed portion  you could check out DryadLINQ  http   research microsoft com en-us projects dryadlinq default aspx

[c#] Map and Reduce in .NET

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