Fast reports use a intermediary object descending from _TFrxDataSet to connect the report engine which the data it prints.
To connect a report to a data source managed by the program itself, you use a TfrxUserDataSet component, which let's you see a data set inside the report, but you manually specify the column names in the Fields (TStrings) property and manage and supply values programatically writing event handlers for the following events:
- OnCheckEOF is functionally equivalent to the OnNeedData, if there's no more to print, you set the EOF var parameter to true
- OnFirst you do whatever you have to do to start walking for the data.
- OnGetValue and OnNewGetValue you provide values for each of the different columns of the current row
- OnNext, OnPrior you move your current row one next or one prior position.
As you see, the row/column concept (a DataSet) is used to provide the data to the report, but you can pull your data from any structure you use to store the result of your calculations (lists, arrays, or any other object/structure/file etc.)
Inside the report, you link the band to this logical DataSet and you use standard components to print the column values of this DataSet.
If you already have the data in a DataSet, for example a in-memory DataSet after your calculations, better use a TfrxDBDataset to directly bind your report to that source of data.