A survey on ranking keyword search results To rank the keyword search results, I'm trying to crack the way the Airbnb algorithm or similar ones work. I'm not asking which features they are using since those are different depending on the business needs. What I'm asking is where can I find a paper/survey/book to see what are the various relevancy metrics in addition to TF-IDF and PageRank? and how can I merge various metrics/algorithms into a single algorithm to sort the search results?

Input: a couple of keywords
Output: a ranked list of options relevant to the input keywords

Anything from links to surveys/books/algorithms/open-source software would work.

Best
There is a research literature on this subject that uses machine learning for ranking; it is often known under the term learning to rank.  I recommend reading the papers on that subject.