Pairwise ranking: A or B?
Ranking twenty things at once is hard; choosing between two is easy. Paste your list, answer one quick question at a time, and get the whole list in order.
Question 1
Which do you prefer?
Keys: 1 or ← left, 2 or → right, U undo.
Your ranking
How the questions are chosen
The tool runs a merge sort, with you as the judge. It ranks small groups first, then merges ranked groups by comparing only their front-runners, so it never asks about a pair whose order already follows from your earlier answers. If you prefer the lake swim to the picnic and the picnic to the hike, it takes the swim over the hike as settled.
For n items it needs at most n⌈log₂ n⌉ − 2⌈log₂ n⌉ + 1 questions. With 10 items that is 25 at most, where comparing every pair would take 45; with 25 items, 94 instead of 300. It often finishes early, because a merge stops as soon as one group runs out. The progress bar compares the questions you have answered with the most that could still be needed.
Undo takes back your last answer: the tool replays all the others. Shuffle mixes the list first, so neighbours in your paste do not always meet first. Your progress is saved in this browser, so you can close the tab and carry on later.
Sources
- Donald E. Knuth, The Art of Computer Programming, Volume 3: Sorting and Searching (2nd ed., 1998), §5.2.4 on merge sorting and §5.3.1 on sorting with the fewest comparisons. Book page
- L. L. Thurstone, A law of comparative judgment, Psychological Review 34(4), 273–286 (1927), the classic paper on judging items in pairs. doi:10.1037/h0070288
Questions
What if I cannot decide between two?
Pick the one you would choose today. When two items are that close, either order is fair, and you can undo if you change your mind.
Why did it not ask about every pair?
Because it assumes your answers are consistent: if A beats B and B beats C, A beats C. That is what keeps the number of questions low.
How many items can I rank?
Up to 100, which takes at most 573 questions. For long lists, rank a shortlist first or sort items into tiers with the tier list maker.