1. A method for automatically generating a displayable report based on a report definition comprising a plurality of user-specified elements, the method being performed by a computer-implemented reporting system, the method comprising: receiving the report definition by a data source interface of the reporting system; parsing the report definition by a report definition component of the reporting system to identify a first user-specified element and a second user-specified element, the first user-specified element specifying a plurality of group buckets and matching criteria respectively associated with each of the group buckets; processing data received from a data source by a grouping component of the reporting system to identify multiple data items included therein, and, for each of the data items: (i) determining if a data value associated with the data item satisfies the matching criteria respectively associated with each of the group buckets, and (ii) if the data value associated with the data item satisfies the matching criteria associated with a particular one of the group buckets, adding the data item to the particular one of the group buckets; identifying one or more empty group buckets from among the plurality of group buckets by the grouping component of the reporting system, each empty group bucket comprising a group bucket within the plurality of group buckets to which no data items have been added; and based on a value of the second user-specified element, selectively performing by the grouping component of the reporting system: including the one or more empty group buckets in the displayable report; or excluding the one or more empty group buckets from the displayable report.