1- Pointwise
Training:
x1 engagement prob
x2 engagement prob
...
then train a model that gives a score for each and sort by score.
2- Pairwise
x1 precedes x2 1
x1 precedes x3 1
x4 precedes x2 0
have n choose 2 training like above and give scores to test set pairs in the same way.
Or you can do learn to rank: https://en.wikipedia.org/wiki/Learning_to_rank
x1 precedes x2 1
x1 precedes x3 1
x4 precedes x2 0
have n choose 2 training like above and give scores to test set pairs in the same way.
Or you can do learn to rank: https://en.wikipedia.org/wiki/Learning_to_rank