@Override
      public int estimate() {
        return histogram.lengthFor(JavaDataModel.get());
      }
Construct a histogram using an algorithm described by Ben-Haim and Tom-Tov.

The algorithm is a heuristic adapted from the following paper:
Yael Ben-Haim and Elad Tom-Tov, "A streaming parallel decision tree algorithm",
J. Machine Learning Research 11 (2010), pp. 849--872. Although there are no approximation
guarantees, it appears to work well with adequate data and a large (e.g., 20-80) number
of histogram bins.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDAFHistogramNumeric.java