Now, I want to allow selection of multiple categories of data. That is, if I have a checkbox which reads "Select all category 1 data", I need to select Category1Data1, Category1Data2 and Category1Data3 in the table. If I have a checkbox which reads "Select all category 3 data" , I need to select Category3Data1 and Category3Data2 in the table.
I've seen this done as sub-checkboxes to a main checkbox, like in a directory tree or parent/child relationship. Select the main checkbox, and all sub-checkboxes are checked, perhaps invisibly; expand the main checkbox to show the sub-checkboxes, select/deselect some of the sub-checkboxes, and the main checkbox shows partially selected, usually indicated by graying the checkbox rather than checking it.
Also, I read somewhere that I could have a combo box with checkboxes to indicate what has to be selected. But is that right? I thought combo boxes are typically used to select one among a list of things. If I have checkboxes for each of the categories in the dropdown of combo box, would that be wrong? Would that be violating UI paradigm?
The combobox selections could be used to define the checkbox selections, as in "All Category 1," "All Category 2," etc. Then you could have a "Partial Category X" combobox item, or a shaded item to show when something less than an entire category is selected. I don't know that this would violate a UI paradigm, but it doesn't seem as intuitive as the main/sub checkbox design.