How Can I Flatten a Tree Structure and Filter by a Property Using LINQ?

Use the linq flat -shaped tree structure and filter according to the attribute

In the field of tree -shaped data, it is often necessary to convert the hierarchical structure to a flat list. Suppose you have a layered classmode with the Parent and Elements attributes, and you want to flatten the trees by extracting all the Mynode instances in a single list. Specifically, you are only interested in getting nodes that are equal to 1 in the Group.

The following linq query provides you with a solution:

<code class="language-c#">var flatList = rootNodes.SelectMany(node => Flatten(node.Elements)).Concat(rootNodes).Where(node => node.group == 1);</code>

The following is its working principle:

selectmany (node ​​= & gt; flatten (node.elements))
• : This method recursively flattened the Elements collection of each MyNode to obtain the flat list of all offspring. Concat (rootnodes)
: Connect the flat list of offspring to the original Mynodes list.
• Where (node ​​= & gt; node.group == 1) : Filter the flat list, which only contains nodes with a group attribute 1.
• In order to improve the readability of the code, please consider using the expansion method for flattening:

Then use your tree calling expansion method, and specify how to retrieve offspring:

<code class="language-c#">public static IEnumerable<T> Flatten<T>(this IEnumerable<T> e, Func<T, IEnumerable<T>> f) => e.SelectMany(c => f(c).Flatten(f)).Concat(e);</code>

Enjoy the benefits brought by the use of linq flat level data!

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