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Hi, that's my blog post. I'm pretty sure about what I wrote here, but may need the authors to chime-in in case I am missing something. I just submited an issue

• lalaland1125 3y ago
  Just wanted to say, thanks for your work debugging this. You have probably saved other researchers an unfathomable amount of time
  • deleted 3y ago
    [deleted]
• syats 3y ago
  Thanks for the replication, this is important. One question, did you try to replicate the other result table (Table 3)? If I understand correctly, top-2 accuracy would be 1 if you have only 2 classes, but it will differ from "normal" accuracy less and less as the number of classes increases (on average). So this shouldn't change the results for table 3 thaaat much as the datasets have large amounts of classes (see table 1). In any case, top-2 accuracy of 0.685 for the 20-newsgroups dataset is pretty neat for a method that doesn't even consider characters as characters[1], let alone tokens, n-grams, embeddings and all the nice stuff that those of use working on NLP have been devoting years to. [1] In my understanding of gzip, it considers only bit sequences, which are not necessarily aligned with words (aka. bytes).
  • ks2048 3y ago
    I haven't yet replicated Table 3 because most of those datasets are much larger and it will take awhile to run (they said the YahooAnswers database took them 6 days). Also, I have only tried the "gzip" row because that is all that is in the github repo they referenced. Yeah, you're right, the more classes there are, probably the lower the effect this will have.
• cs702 3y ago
  Whoa, I just read your post and saw this: > tldr: it is reporting a top-2 accuracy rather than a kNN(k=2) accuracy If the accuracy figures shown for other models are top-1, that's a pretty significant mistake, hopefully an innocent one. Thank you for doing this and sharing your findings! --- Previous discussion on HN: https://news.ycombinator.com/item?id=36707193 https://news.ycombinator.com/item?id=36707193
  • DebtDeflation 3y ago
    Also: >k=2 is a bit of an odd choice for kNN classification That's an understatement. Choosing an even number for any sort of voting algorithm doesn't make much sense, choosing 2 specifically probably makes the least sense of all.
    • spi 3y ago
      Yeah that is a big red flag - as the OP mentions, there is basically no way of making k=2 statistically different from k=1, that's why nobody uses it. I suppose the authors just tried many different k and selected k=2 because it performed surprisingly well (likely due to the bug the OP found out). But if the results were significantly better than k=1 or k=3, it's a bit weird the authors never double checked why that was the case. I guess it can be one of those things you settle on early in the overall process with a few experiments, and just take for granted afterwards, never checking it again, but still, it sounds like something that should pop out at some point while writing the paper...?
    • 1024core 3y ago
      True. You want to always use an odd number so there are no ties. I'm guessing they were trying a parameter sweep, and found that (thanks to the bug) they got the best results for K=2. This too is problematic in its own sense.
      • ks2048 3y ago
        Yes, agreed. One small point: for the multi-class case (more than just two classes), which include all the datasets here, you can still get ties for odd k. e.g. k=3, you can get 1 vote each for 3 different classes, etc.
• p1esk 3y ago
  Did you try contacting the authors before you went public with your discovery?
  • _b 3y ago
    We're adult enough to have discussions like this in public. They are healthy to have. People make mistakes. Kudos to the original authors for releasing the source code so people could inspect and replicate their results.
    • returningfory2 3y ago
      I agree, and just want to add: nowadays it's super common for researchers to widely publicize their new work on social media. The blog post here even mentions "Table 5 from the paper was often included in tweets". In this context of sharing your results very publicly, it seems only fair that rebuttals would be very public, too. Otherwise researchers would be highly incentivized to very publicly publish weak results because they would get a lot of positive publicity when they share the results, but not much negative publicity when the weaknesses are found and shared.
  • jarym 3y ago
    It isn't a security issue and doesn't warrant responsible disclosure so why would op be expected to?
  • ks2048 3y ago
    I did not, but I see why that could be a better approach. I mainly am trying to be more open with little side projects I do, so wanting to start blogging what I'm working on. Also, this paper was beiung widely discussed so thought this would be one more entry in that.
• eyegor 3y ago
  You may want to consider adding a note to the top. Seems like a lot of people are lazily skimming/reading the headline and see it as "gzip paper full of beans, gzip approach sucks" when really I see this as "gzip approach not better than dnn models but mostly competes and much cheaper to run". The paper is still solid.
  • marcinzm 3y ago
    >gzip approach not better than dnn models but mostly competes and much cheaper to run Does it? It looks to do worse than FastText in all benchmarks and kNN is not a cheap algorithm to run so it might actually be slower than FastText. edit: It looks like FastText takes 5 seconds to train on the Yahoo Answers data set while the gzip approach took them 6 days. So definitely not faster.
    • tensor 3y ago
      FastText isn't a LLM, it's a token embedding model with a simple classifier on top.
      • marcinzm 3y ago
        Sure but it's existence means the statement is really "gzip approach not better than dnn models, and doesn't compete or be cheaper to run than previous models like FastText." That's not a very meaningful value statement for the approach (although why gzip is even half-decent might be a very interesting research question).
    • eyegor 3y ago
      I'm not familiar with most of these models in detail, but training time is generally less interesting than inference time to me. I don't care if it takes a month to train on $10k of gpu rentals if it can be deployed and run on a raspberry pi. I should definitely look into fasttext though.
      • amluto 3y ago
• deleted 3y ago
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• ginbazinga 3y ago
  Hi, I'm the first author of the paper and I read your blog post. The reason I chose k=2 is because it's recommended to use n^{1/2} and I wanted to pick a k that's compatible with 5-shot setting. But you are right this is a bit odd. As I mentioned in both the paper and the twitter, different values of k will affect the result and I reported the _max_ result we can get so it does mean an ideal situation when the guess is always right. I also use this strategy for W2V and SentBERT. But it doesn't make the result top2 accuracy. As far as I know, top2 accuracy means in the top2 predicted classes, either one is correct, we score. However, as you mentioned, in knn when k=2, there is a situation when the 2 nearest neighbours point to the same class - we are missing another class candidate if reporting top2 accuracy. But I would love to add results for different strategies and different k values when I upload newest version to arxiv when I have time. The strategy of "decrement" you mentioned in the blog is really nice and I would love to add it to the repo if you want. I apologize for the short and late reply; I haven't checked the repo yet. I'm preparing for tomorrow's thesis defence and will reply & resolve the issue when I finish.