17. The media of claim 16 , further comprising instructions that when executed by the at least one processor cause the at least one processor to: generate a vector for each content item in the plurality of content items, a content item's vector identifying the content item and, for each topic in the plurality of content item topics, the relevance of the topic to the content item.
16. The media of claim 15 , further comprising instructions that when executed by the at least one processor cause the at least one processor to: identify, for each content item in the plurality of content items, each topic's relevance to the content item using a topic model and token occurrences in the content item, the topic model identifying a probabilistic correspondence between token occurrences and the plurality of content item topics.