使用SelectMany()的不同方式 [英] Different ways of using SelectMany()

问题描述

我想知道如何使用SelectMany().似乎有很多争论，根据我自己的研究，我注意到SelectMany()可能是所有其他选择操作的父亲".

I'd like to know how to use SelectMany(). It seems to take so many arguments and from my own research I noticed that SelectMany() might be the 'father' of all other select operations.

推荐答案

选择许多"允许您从查询源中选择一个IEnumerable< T>属性.集合，而不是返回集合(IEnumerable< IEnumerable< T>>>)的集合，而是将集合扁平化为单个集合.

Select many allows you to select a property from your query source that is an IEnumerable<T> collection, but instead of returning a collection of collections (IEnumerable<IEnumerable<T>>) it will flatten the collections into a single collection.

下面是一个示例，您可以运行该示例来演示Select和SelectMany之间的区别:

Here's an example that you can run to demonstrate the differences between Select and SelectMany:

//set up some data for our example
var tuple1 = new { Name = "Tuple1", Values = new int [] { 1, 2, 3 } };
var tuple2 = new { Name = "Tuple2", Values = new int [] { 4, 5, 6 } };
var tuple3 = new { Name = "Tuple3", Values = new int [] { 7, 8, 9 } };

//put the tuples into a collection
var tuples = new [] { tuple1, tuple2, tuple3 };

//"tupleValues" is an IEnumerable<IEnumerable<int>> that contains { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } }
var tupleValues = tuples.Select(t => t.Values);

//"tupleSelectManyValues" is an IEnumerable<int> that contains { 1, 2, 3, 4, 5, 6, 7, 8, 9 }
var tupleSelectManyValues = tuples.SelectMany(t => t.Values);

通过使用SelectMany，您可以更轻松地查询子集合中的值.

By using SelectMany you make it easier to query values within child collections.

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