Corrected bug in SlopeOne and added benchmarks

NicolasHug · Dec 15, 2016 · ab67f40 · ab67f40
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diff --git a/README.md b/README.md
@@ -142,6 +142,7 @@ GHz, 4Go RAM.
 | [KNNBaseline](http://surprise.readthedocs.io/en/latest/knn_inspired.html#surprise.prediction_algorithms.knns.KNNBaseline)     |  .9306 |  .7334 |    44    |
 | [SVD](http://surprise.readthedocs.io/en/latest/matrix_factorization.html#surprise.prediction_algorithms.matrix_factorization.SVD)             |  .9392 |  .7409 |    46    |
 | [SVD++](http://surprise.readthedocs.io/en/latest/matrix_factorization.html#surprise.prediction_algorithms.matrix_factorization.SVDpp)             |  .9200 |  .7253 |    31min    |
+| [Slope One](http://surprise.readthedocs.io/en/latest/slope_one.html#surprise.prediction_algorithms.slope_one.SlopeOne)             |  .9454 |  .7430 |    25    |
 
 
 |  [Movielens 1M](http://grouplens.org/datasets/movielens/1m) |  RMSE  |   MAE  | Time (min) |
@@ -152,6 +153,8 @@ GHz, 4Go RAM.
 | [KNNWithMeans](http://surprise.readthedocs.io/en/latest/knn_inspired.html#surprise.prediction_algorithms.knns.KNNWithMeans)    |  .9292 |  .7386 |    22    |
 | [KNNBaseline](http://surprise.readthedocs.io/en/latest/knn_inspired.html#surprise.prediction_algorithms.knns.KNNBaseline)     |  .8949 | .7063 |    44    |
 | [SVD](http://surprise.readthedocs.io/en/latest/matrix_factorization.html#surprise.prediction_algorithms.matrix_factorization.SVD)             |  .8936 |  .7057 |    7    |
+| [Slope One](http://surprise.readthedocs.io/en/latest/slope_one.html#surprise.prediction_algorithms.slope_one.SlopeOne)             |  .9065 |  .7144 |    8    |
+
 
 Documentation, Getting Started
 ------------------------------

diff --git a/surprise/prediction_algorithms/slope_one.pyx b/surprise/prediction_algorithms/slope_one.pyx
@@ -97,6 +97,7 @@ class SlopeOne(AlgoBase):
         # i and j).
         Ri = [j for (j, _) in self.trainset.ur[u] if self.freq[i, j] > 0]
         est = self.user_mean[u]
-        est += sum(self.dev[i, j] for j in Ri) / len(Ri)
+        if Ri:
+            est += sum(self.dev[i, j] for j in Ri) / len(Ri)
 
         return est