Hi, to access the data (DataCells) in the BufferedDataTable, you need to iterator over the table. The iterator returns DataRow objects which then contain DataCells of a particular type. Note, you can figure out the type before by parsing the DataTableSpec:

DataTableSpec spec = ...
for (int i = 0; i < spec.getNumColumns(); i++) {
DataColumnSpec cspec = spec.getColumnSpec(i);
DataType type = cspec.getType();
if (type.isCompatible(ComplexNumberValue.class)) {
...
}
}

Now, where you figured out which columns are of type ComplexNumberValue, you can easily cast each object to ComplexNumberValue and access the real and imaginary part. In a last step you need to write these values into your own data structure and call your FF algorithm.

BufferedDataTable data = ...
for (DataRow row : data) {
for (DataCell cell : row) {
// handle missing values
if (!cell.isMissing()) {
// we assume all columns are of type ComplexNumberValue
// but you will need to check this before
ComplexNumberValue value = (ComplexNumberValue) cell;
double real = value();
double imag = value.getImaginaryValue();
// store real and imag into your data structure
} else {
...
}
}
}

[...] ok, some more coding :-) In order to write (new) data to the node's output, you need to create a BufferedDataContainer to which you can add rows containing DataCell objects (the actual data). A first step is to create the names and types of the output table using the DataColumnSpecCreater which generates DataColumnSpec objects which are then used to initialize a DataTableSpec. The attached example shows how to write an array of doubles to the output. Please feel free to adapt this code snippet to fit your needs:

BufferedDataTable[] execute(...) {
// contains the result of the FF algorithm
double[][] data = ...
// create column names and types of the output table
DataColumnSpec[] cspec = new DataColumnSpec[data.length];
for (int i = 0; i < cspec.length; i++) {
cspec[i] = new DataColumnSpecCreator(
"Col" + i, DoubleCell.TYPE).createSpec();
}
DataTableSpec spec = new DataTableSpec(cspec);
// write DataRow objects into this container
BufferedDataContainer buf = exec.createDataContainer(spec);
if (data.length > 0) {
for (int i = 0; i < data[0].length; i++) {
DataCell[] cells = new DataCell[data.length];
for (int j = 0; j < cells.length; j++) {
cells[j] = new DoubleCell(data[j][i]);
}
// generate a new row key or use the one from the input data
DataCell rowKey = new StringCell("Row" + i);
// add each row to the buffer
buf.addRowToTable(new DefaultRow(rowKey, cells));
}
}
buf.close();
return new BufferedDataTable[]{buf.getTable()};
}