code: public static RegressionDataSet loadR(Reader reader, double sparseRatio, int vectorLength) throws IOException
      {
          return loadR(reader, sparseRatio, vectorLength, DataStore.DEFAULT_STORE);
      }
docs: Loads a new regression data set from a LIBSVM file, assuming the label is
  a numeric target value to predict.
  
  @param reader the reader for the file to load
  @param sparseRatio the fraction of non zero values to qualify a data
  point as sparse
  @param vectorLength the pre-determined length of each vector. If given a
  negative value, the largest non-zero index observed in the data will be
  used as the length.
  @return a regression data set
  @throws IOException