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https://issues.apache.org/jira/browse/MAHOUT-1739?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14585511#comment-14585511
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lariven commented on MAHOUT-1739:
---------------------------------
"mahout spark-itemsimilariy" really output a symmetric matrix not triangular
matrix. The inconsistency may confuse many people. Or maybe someone is using
"mahout itemsimilariy" without knowing that it's a triangular matrix. :(
> maxSimilarItemsPerItem param of ItemSimilarityJob doesn't behave correct
> ------------------------------------------------------------------------
>
> Key: MAHOUT-1739
> URL: https://issues.apache.org/jira/browse/MAHOUT-1739
> Project: Mahout
> Issue Type: Bug
> Components: Collaborative Filtering
> Affects Versions: 0.10.0
> Reporter: lariven
> Labels: easyfix, patch
> Attachments: fix_maxSimilarItemsPerItem_incorrect_behave.patch
>
>
> the output similar items of ItemSimilarityJob for each target item may exceed
> the number of similar items we set to maxSimilarItemsPerItem parameter. the
> following code of ItemSimilarityJob.java about line NO. 200 may affect:
> if (itemID < otherItemID) {
> ctx.write(new EntityEntityWritable(itemID, otherItemID), new
> DoubleWritable(similarItem.getSimilarity()));
> } else {
> ctx.write(new EntityEntityWritable(otherItemID, itemID), new
> DoubleWritable(similarItem.getSimilarity()));
> }
> Don't know why need to switch itemID with otherItemID, but I think a single
> line is enough:
> ctx.write(new EntityEntityWritable(itemID, otherItemID), new
> DoubleWritable(similarItem.getSimilarity()));
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