code: public static JavaRDD<List<Writable>> zeromeanUnitVariance(Schema schema, JavaRDD<List<Writable>> data) {
          return zeromeanUnitVariance(schema, data, Collections.<String>emptyList());
      }
docs: Normalize by zero mean unit variance
  
  @param schema the schema to use
  to create the data frame
  @param data   the data to normalize
  @return a zero mean unit variance centered
  rdd