I took Information Retrieval 101 in grad school and it was an interesting course. If you're curious to learn more, term frequency–inverse document frequency (tf–idf) is a good place to start. The underlying idea is surprisingly simple.
Likewise with the core of Google's (original) ranking algorithm, PageRank, which is inspired by ideas like h-index.
Also, the "standard" book which we used is quite readable: Introduction to Information Retrieval by Manning, et al.
Skim it once to collect vocabulary, then use it as a reference for IR algorithms.
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