code: @Override
  	public String convert(SIFInteraction inter)
  	{
  		String s = inter.toString();
  
  		for (OutputColumn column : columns)
  		{
  			s += "\t" + column.getColumnValue(inter);
  		}
  
  		return s;
  	}
docs: Prepares the line in the output file for the given interaction.
  @param inter the interaction
  @return output line.