[jira] [Updated] (MAHOUT-1958) CityBlockSimilarity.itemSimilarities can overflow

[Hao Zhong (JIRA)]

     [ 
https://issues.apache.org/jira/browse/MAHOUT-1958?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
 ]

Hao Zhong updated MAHOUT-1958:
------------------------------
    Status: Patch Available  (was: Open)

diff --git 
a/mr/src/main/java/org/apache/mahout/cf/taste/impl/similarity/CityBlockSimilarity.java
 
b/mr/src/main/java/org/apache/mahout/cf/taste/impl/similarity/CityBlockSimilarity.java
index 88fbe58..760f10c 100644
--- 
a/mr/src/main/java/org/apache/mahout/cf/taste/impl/similarity/CityBlockSimilarity.java
+++ 
b/mr/src/main/java/org/apache/mahout/cf/taste/impl/similarity/CityBlockSimilarity.java
@@ -53,9 +53,9 @@
   @Override
   public double itemSimilarity(long itemID1, long itemID2) throws 
TasteException {
     DataModel dataModel = getDataModel();
-    int preferring1 = dataModel.getNumUsersWithPreferenceFor(itemID1);
-    int preferring2 = dataModel.getNumUsersWithPreferenceFor(itemID2);
-    int intersection = dataModel.getNumUsersWithPreferenceFor(itemID1, 
itemID2);
+    long preferring1 = dataModel.getNumUsersWithPreferenceFor(itemID1);
+    long preferring2 = dataModel.getNumUsersWithPreferenceFor(itemID2);
+    long intersection = dataModel.getNumUsersWithPreferenceFor(itemID1, 
itemID2);
     return doSimilarity(preferring1, preferring2, intersection);
   }
 
@@ -90,8 +90,8 @@
    * @param pref2        number of non-zero values in right vector
    * @param intersection number of overlapping non-zero values
    */
-  private static double doSimilarity(int pref1, int pref2, int intersection) {
-    int distance = pref1 + pref2 - 2 * intersection;
+  private static double doSimilarity(long pref1, long pref2, long 
intersection) {
+    long distance = pref1 + pref2 - 2 * intersection;
     return 1.0 / (1.0 + distance);
   }
 


> CityBlockSimilarity.itemSimilarities can overflow
> -------------------------------------------------
>
>                 Key: MAHOUT-1958
>                 URL: https://issues.apache.org/jira/browse/MAHOUT-1958
>             Project: Mahout
>          Issue Type: Bug
>          Components: Math
>    Affects Versions: 1.0.0
>            Reporter: Hao Zhong
>
> The CityBlockSimilarity.itemSimilarities method has the following code:
> {code:title=CityBlockSimilarity.java|borderStyle=solid}
>       int preferring2 = dataModel.getNumUsersWithPreferenceFor(itemID2s[i]);
>       int intersection = dataModel.getNumUsersWithPreferenceFor(itemID1, 
> itemID2s[i]);
> {code}
> Here, the two methods return long values, and can overflow. Indeed, 
> LogLikelihoodSimilaritydoItemSimilarity once had the same problem. The fixed 
> code is
> {code:title=LogLikelihoodSimilaritydoItemSimilarity.java|borderStyle=solid}
>     long preferring1 = dataModel.getNumUsersWithPreferenceFor(itemID1);
>     long numUsers = dataModel.getNumUsers();
> {code}
> Please refer to MAHOUT-738 for details.



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