Regarding the Grouping feature: Often, the OpenOffice documentation has more information on certain features, than the LibreOffice docs. Take care that OO and LO have developed independently since some years, but basic functionality is still the same. The OO docs have some info on hiding/showing data.
In your case, using a
AutoFilter is the best way to hide certain empty rows. First, you should add a (quite simple) header row to your data:
Now, just select menu
AutoFilter - this will add some small filter buttons to the header row. For example, the filter button for col C will show the following filter dialog:
To hide row 3, row 5 and so on, click on the
AutoFilter button of Col
C and select
Not empty. This will hide every row where the
C cell is empty.
To keep only rows 2, 8 and 14 (with text
Gamma), use the
AutoFilter button on Col
A and select
Grouping or outlining data is quite easy if there's a clear structure in the data. For example, assuming that your first example contains sum rows for each of the three groups (E7, E13 and E19 are each the sum of the five cells above):
In such a case, LO calc is able to determine the structure and to auto-outline the data. In this example, just select A2:E19 and select Menu Data -> Group and Outline -> AutoOutline. Calc will create three groups, just based on the sum function in col E:
So, it depends on the data and the use case when choosing between grouping and filtering data.