C# .NET 中的映射和缩减
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Map and Reduce in .NET
提问by Developer
What scenarios would warrant the use of the "Map and Reduce" algorithm?
哪些场景可以保证使用“ Map and Reduce”算法？
Is there a .NET implementation of this algorithm?
这个算法有 .NET 实现吗？
采纳答案by Tony
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 和 Reduce 的 Linq 等价物：如果您有幸拥有 linq，那么您无需编写自己的 map 和 reduce 函数。C# 3.5 和 Linq 已经有了它，尽管名称不同。
Map is
Select:Enumerable.Range(1, 10).Select(x => x + 2);Reduce is
Aggregate:Enumerable.Range(1, 10).Aggregate(0, (acc, x) => acc + x);Filter is
Where:Enumerable.Range(1, 10).Where(x => x % 2 == 0);
地图是
Select：Enumerable.Range(1, 10).Select(x => x + 2);减少是
Aggregate：Enumerable.Range(1, 10).Aggregate(0, (acc, x) => acc + x);过滤器是
Where：Enumerable.Range(1, 10).Where(x => x % 2 == 0);
回答by Joel Martinez
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.
非常适合 mapreduce 风格解决方案的问题类别是聚合问题。从数据集中提取数据。在 C# 中，可以利用 LINQ 以这种方式进行编程。
From the following article: http://codecube.net/2009/02/mapreduce-in-c-using-linq/
来自以下文章：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.
GroupBy 方法充当映射，而 Select 方法负责将中间结果减少到最终结果列表中。
var wordOccurrences = words
.GroupBy(w => w)
.Select(intermediate => new
{
Word = intermediate.Key,
Frequency = intermediate.Sum(w => 1)
})
.Where(w => w.Frequency > 10)
.OrderBy(w => w.Frequency);
For the distributed portion, you could check out DryadLINQ: http://research.microsoft.com/en-us/projects/dryadlinq/default.aspx
对于分布式部分，您可以查看 DryadLINQ：http://research.microsoft.com/en-us/projects/dryadlinq/default.aspx
回答by CsUtil.com
Since I never can remember that LINQ calls it Where, Selectand Aggregateinstead of Filter, Mapand Reduceso I created a few extension methods you can use:
因为我从来不记得是LINQ调用它Where，Select并Aggregate代替Filter，Map并Reduce让我创建了一些扩展方法，你可以使用：
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:
来自https://github.com/cs-util-com/cscore#ienumerable-extensions 的更多细节：
