DataGraph does not have way to import from subfolders, but ImageTank can do this. If you download ImageTank, you can use that to combine the data and then copy and paste to DataGraph.
I set up an example where there is a folder with three subfolders, each one contains a simple csv.
Drag the folder ‘All Data’ from the Finder and Drop it on the left side of the ImageTank user interface.
That creates an object. Expand the object and click the check box for ‘Go into sub folders’. Then the number of files in the subfolders will be shown below the name. From the gear menu, select ‘Read Table from Text file – Simple’.
That creates a second object. From the second object, open the side pop up window and click the button ‘All’ as shown below. In the future this will be done automatically, but this loads the data.
Click the variable monitor (indicated with the red arrow) and you will see the data. Again use the gear menu and select to Combine time values.
Now you have a third object with all the data combined into one table. Click the DataGraph icon to copy the data to the clipboard, and then paste into DataGraph.
ImageTank stores data in tables, which is different from DataGraph that stores data in columns. That is why you have an object for each table or set of tables.
Let us know if this helps or any problems you encounter.