Disclosed are systems, apparatus, methods and computer-readable storage media for combining topic suggestions from different topic sources to assign to textual data items. In some implementations, a first automated topic source provides one or more first topic suggestions to associate with a textual data item. Each first topic suggestion has a respective first characteristic, which can be adjusted. A second automated topic source provides one or more second topic suggestions to associate with the textual data item. Each second topic suggestion has a respective second characteristic, which can be adjusted. The first and second topic suggestions are combined to define a combined list. A reference value is determined or retrieved to impact ordering of the topic suggestions in the combined list.