https://en.m.wikipedia.org/wiki/Learning_to_rank
https://docs.aws.amazon.com/elasticsearch-service/latest/developerguide/learning-to-rank.html
https://github.com/dmlc/xgboost/tree/master/demo/rank
https://github.com/o19s/es-tmdb
https://github.com/o19s/elasticsearch-learning-to-rank
https://github.com/o19s/elasticsearch-ltr-demo
https://github.com/o19s/hello-ltr
https://github.com/ehsangolshani/ranklib-demo
https://github.com/andrew-sn/sltr_demo
https://blog.csdn.net/ctrip_tech/article/details/103519193
https://www.infoq.cn/article/we-are-bringing-learning-to-rank-to-elasticsearch
https://github.com/o19s/rated-ranking-evaluator
https://github.com/o19s/relevant-search-book
https://github.com/o19s/word2vec-experiments
https://github.com/o19s/splainer