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  1. PO
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    <p>Here's my solution that so far has proven to avoid duplicate results. It's in C# (for Lucene.Net) but I've started it from the Java sample so it should be easily converted back.</p> <p>The trick I used was a unique ID per search that stays unchanged while the user clicks on pagination. I already had this unique ID that I used for reporting purposes. I initialize it when the user clicks the search button and then I pass it encrypted in the query string. It's finally passed as the seed parameter in RandomOrderFieldComparatorSource (actually it's ID.GetHashCode()).</p> <p>What this means is I use the same series of random numbers for same search, so each docId gets the same sorting index even when users navigate to other result pages.</p> <p>One more note, <em>slots</em> could probably be a vector equal to pagesize.</p> <pre><code>public class RandomOrderFieldComparator : FieldComparator { Random random; List&lt;int&gt; slots = new List&lt;int&gt;(); Dictionary&lt;int, int&gt; docSortIndeces = new Dictionary&lt;int, int&gt;(); public RandomOrderFieldComparator(int? seed) { random = seed == null ? new Random() : new Random(seed.Value); } private int bottom; // Value of bottom of queue public override int Compare(int slot1, int slot2) { // TODO: there are sneaky non-branch ways to compute // -1/+1/0 sign // Cannot return values[slot1] - values[slot2] because that // may overflow int v1 = slots[slot1]; int v2 = slots[slot2]; if (v1 &gt; v2) { return 1; } else if (v1 &lt; v2) { return -1; } else { return 0; } } public override int CompareBottom(int doc) { // TODO: there are sneaky non-branch ways to compute // -1/+1/0 sign // Cannot return bottom - values[slot2] because that // may overflow int v2 = GetDocSortingIndex(doc); if (bottom &gt; v2) { return 1; } else if (bottom &lt; v2) { return -1; } else { return 0; } } public override void Copy(int slot, int doc) { if (slots.Count &gt; slot) { slots[slot] = GetDocSortingIndex(doc); } else { slots.Add(GetDocSortingIndex(doc)); } //slots[slot] = GetDocSortingIndex(doc); } public override void SetBottom(int bottom) { this.bottom = slots[bottom]; } public override System.IComparable Value(int slot) { return (System.Int32)slots[slot]; } public override void SetNextReader(IndexReader reader, int docBase) { } int GetDocSortingIndex(int docId) { if (!docSortIndeces.ContainsKey(docId)) docSortIndeces[docId] = random.Next(int.MinValue, int.MaxValue); return docSortIndeces[docId]; } } </code></pre>
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    1. POLucene 2.9.2: How to show results in random order?
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    1. PTAnswer
    1. USBogdan Litescu
    1. USBogdan Litescu
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    1. VO
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      1. VTUpMod
    1. COThanks, but I meant duplicate results after ONE SINGLE query. Pagination is not part of my question. But nice approach for your pagination solution (is probably important when the index changes quite often).
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      1. PO
      1. USbasZero
    2. COSome customers of mine also reported duplicate results so I ended up reimplementing the RandomOrderScoreDocComparator starting from IntComparator from Lucene.Core. I've updated my post with new code.
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      1. USBogdan Litescu
 

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