Merge branch 'conradsnicta-master'

HISTORY.md

@@ -33,6 +33,9 @@
 
   * Improve KDE pruning by reclaiming not used error tolerance (#1954, #1984).
 
+  * Optimizations for sparse matrix accesses in z-score normalization for CF
+    (#1989).
+
 ### mlpack 3.1.1
 ###### 2019-05-26
   * Fix random forest bug for numerical-only data (#1887).

src/mlpack/methods/cf/normalization/z_score_normalization.hpp

@@ -88,15 +88,20 @@ class ZScoreNormalization
     }
 
     // Subtract mean from existing rating and divide it by stddev.
+    // TODO: consider using spmat::transform() instead of spmat iterators
+    // TODO: http://arma.sourceforge.net/docs.html#transform
     arma::sp_mat::iterator it = cleanedData.begin();
     arma::sp_mat::iterator it_end = cleanedData.end();
     for (; it != it_end; ++it)
     {
-      *it = (*it - mean) / stddev;
+      double tmp = (*it - mean) / stddev;
+
       // The algorithm omits rating of zero. If normalized rating equals zero,
       // it is set to the smallest positive double value.
-      if (*it == 0)
-        *it = std::numeric_limits<double>::min();
+      if (tmp == 0)
+        tmp = std::numeric_limits<double>::min();
+
+      *it = tmp;
     }
   }