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POHow to implement a non-trivial map between collections in Reactive Extensions?
 

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    <p>I would like to implement a <strong>map from selected objects</strong> to <strong>property entries</strong> in property editor. For example like in Visual Studio xaml editor.</p> <p>The target map is something like this (or maybe using ReactiveCollection from ReactiveUI?)</p> <pre class="lang-none prettyprint-override"><code> Selected objects Filled categories to display in PropertyEditor ------------------------- --------------------------------------- ObservableCollection&lt;obj&gt; -&gt; ObservableCollection&lt;Category&gt; </code></pre> <p>The map in plain English:</p> <ol> <li>Collect all unique property types from objects</li> <li>Group by category (e.g. Text, Layout)</li> <li>Add/Remove categories as necessary to reflect selected objects</li> <li>Add/Remove properties from existing categories as necessary</li> </ol> <p>The challenge is to have declarative/functional code without add/remove branches. (I do already have an imperative/event based code which is quite ugly and error prone.)</p> <p>I think we could assume that Category and Property collections are sets with the usual operations: Union, Substract, and IsMember.</p> <p>The inspiration is the code from <a href="http://www.reactiveui.net/" rel="nofollow">ReactiveUI</a> by Paul Betts which is beatiful for simple one-to-one map:</p> <pre class="lang-cs prettyprint-override"><code>var Models = new ReactiveCollection&lt;ModelClass&gt;(); var ViewModels = Models.CreateDerivedCollection(x =&gt; new ViewModelForModelClass(x)); // Now, adding / removing Models means we // automatically have a corresponding ViewModel Models.Add(new Model(”Hello!”)); ViewModels.Count(); &gt;&gt;&gt; 1 </code></pre> <p>Using Seq and F# the straightforward nonobservable map would look like this:</p> <pre class="lang-ml prettyprint-override"><code>selectedObjects |&gt; Seq.collect GetProperties |&gt; Seq.unique |&gt; Seq.groupBy GetPropertyCategory |&gt; Seq.map (fun categoryName properies -&gt; CreateCategory(properties)) </code></pre> <p>The above code is fine in theory but in practice it would recreate all the view models from scratch on each change in selected objects. What I would love to achieve with Rex is to have the version of the above map <strong>with incremental updates</strong>, so the WPF will update only the changed parts of the GUI.</p>
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