/**
  * Append a column of value type INT as the last column of the data frame. The given array is
  * wrapped but not copied and hence might be updated in the future.
  *
  * @param col
  */
 public void appendColumn(long[] col) {
   ensureColumnCompatibility(col.length);
   _schema.add(ValueType.INT);
   _coldata.add(new LongArray(col));
   _numRows = col.length;
 }
 /**
  * Append a column of value type DOUBLE as the last column of the data frame. The given array is
  * wrapped but not copied and hence might be updated in the future.
  *
  * @param col
  */
 public void appendColumn(double[] col) {
   ensureColumnCompatibility(col.length);
   _schema.add(ValueType.DOUBLE);
   _coldata.add(new DoubleArray(col));
   _numRows = col.length;
 }
 /**
  * Append a column of value type BOOLEAN as the last column of the data frame. The given array is
  * wrapped but not copied and hence might be updated in the future.
  *
  * @param col
  */
 public void appendColumn(boolean[] col) {
   ensureColumnCompatibility(col.length);
   _schema.add(ValueType.BOOLEAN);
   _coldata.add(new BooleanArray(col));
   _numRows = col.length;
 }