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    <p>It's fairly easy to implement on your own:</p> <pre class="lang-dart prettyprint-override"><code>Iterable distinct(Iterable i) { var set = new Set(); return i.where((e) { var isNew = !set.contains(e); set.add(e); return isNew; }); </code></pre> <p>It'd be even nicer if <code>Set.add()</code> returned a bool that indicated whether the set was modified:</p> <pre class="lang-dart prettyprint-override"><code>Iterable distinct(Iterable i) { var set = new Set(); return i.where((e) =&gt; set.add(e)); } </code></pre> <p>You can file feature request bugs of course.</p> <p>Edit: As Florian points out, the above solution only works if the returned <code>Iterable</code> is only used once. Subsequent uses will return <code>Iterator</code>s with no elements, because even element has been seen already on the first use.</p> <p>To solve this we need to keep a visited set for every <code>Iterator</code> created from the returned <code>Iterable</code>, not just one for the <code>Iterable</code>. We can do that by creating <code>Iterable</code> and <code>Iterator</code> subclasses like with <code>WhereIterable</code>/<code>WhereIterator</code>:</p> <pre class="lang-dart prettyprint-override"><code>Iterable distinct(Iterable i) =&gt; new DistinctIterable(i); class DistinctIterable&lt;E&gt; extends Iterable&lt;E&gt; { final Iterable&lt;E&gt; _iterable; DistinctIterable(this._iterable); Iterator&lt;E&gt; get iterator { return new DistinctIterator&lt;E&gt;(_iterable.iterator); } } class DistinctIterator&lt;E&gt; extends Iterator&lt;E&gt; { final Iterator&lt;E&gt; _iterator; final Set&lt;E&gt; _visited = new Set&lt;E&gt;(); DistinctIterator(this._iterator); bool moveNext() { while (_iterator.moveNext()) { if (!_visited.contains(_iterator.current)) { _visited.add(_iterator.current); return true; } } return false; } E get current =&gt; _iterator.current; } </code></pre> <p>Yes, this is much longer, but it'll work correctly with many-use finite <code>Iterable</code>s and one-use infinite <code>Iterable</code>s. The infinite iterable use case could easily have problems with memory, which is an argument for not including it in the core lib and forcing developers to make some decisions about what exactly they need.</p>
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    1. POHow to remove duplicate elements in a list while preserving order?
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    1. PTAnswer
    1. USJustin Fagnani
    1. USJustin Fagnani
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    1. POHow to remove duplicate elements in a list while preserving order?
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      1. VTUpMod
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    1. COthx for the answer. I think i needed distinct() like 1 year ago and i wrote my own removeDuplicates(). I thought they need some time to implement the "official" dart-distinct(). And now I hear it is still not available. I just wonder: why?
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      1. USGero
    2. COThere are a lot of things that aren't there yet. Did you file a feature request?
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      1. USJustin Fagnani
    3. COThe solution works, but only, if the iterator is used only once.
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      1. USFlorian Loitsch
 

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