Classifying Hacker News Titles

# Introduction¶

In my last essay I described the problem of filtering Hacker News to produce a purified feed. My viewpoint, motivation and idea of what constitutes a "good" posting is described there, so read it if you're interested.

Since then I've developed a classifier that produces an enriched feed. In this article I'll describe the classifier, show you the results, and show some evaluation information.

The overall methodology is like that used in the machine learning literature, where I split a labeled sample of articles into a training and a test set, create a model, and then test the model by comparing predictions it makes to my own evaluations.

Out[79]:

what's unusual about this article is that it applies this technique to a problem that I formulated from the beginning, applying the evaluation methodology to confirm fitness to purpose, as opposed to entering into a competition to get better results on a pre-existing data set.

Along the way I will explain how my model works, what the output that I see looks like, and how some changes to the system affect the quality of results, with an eye to understanding what the training requirements for a more general feed classifier would be.

## A working model¶

Here is the information that I have for an article in the training set:

stories/15608169
relevant True
href http://dark.nightmare.com/rushing/irken/irken/lang.html
title Irken – A statically-typed Scheme with row polymorphism
hnuser jokermatt999
words [irken, –, a, statically-typed, scheme, with, row, polymorphism]

## Input Features¶

My classifier only looks at tokens that appear in the title. The tokens are produced by the nltk_tokenize function: some of these tokens are words, others are punctuation. It is common in this kind of work to eliminate the most common words (stopwords) and to eliminate words that are less common (because these are not well sampled.) For now, I keep everything, because the classifier I am using (logistic regression) can handle a large number of features, both in terms of execution speed and in terms of realistically estimating how much weight to put on both highly common and highly rare features.

For each word in the vocabulary, there is a feature: the value of that feature is 1 if the word is present in the title, and 0 if it is not. The input matrix looks like:

index the : a to and of for in , ... giants campus moocs autumn jihadist recursive zalando norcal deliver apocalypse
story
stories/15275572 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15624497 0 1 1 1 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15359134 1 0 0 0 0 1 0 1 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15454882 1 0 0 0 0 1 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15523617 0 0 1 0 0 0 0 0 1 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15436767 0 0 0 1 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15501411 0 1 0 0 0 0 1 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15277669 0 0 0 0 1 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15415733 0 0 0 0 1 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15284015 0 0 0 0 0 0 0 1 0 0 ... 0 0 0 0 0 0 0 0 0 0
... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ...
stories/15452637 1 0 0 0 0 0 0 0 0 1 ... 0 0 0 0 0 0 0 0 0 0
stories/15597265 0 0 0 0 0 1 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15602620 0 0 1 0 0 0 0 0 0 1 ... 0 0 0 0 0 0 0 0 0 0
stories/15457218 0 1 0 0 0 0 1 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15410558 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15411600 0 0 0 0 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15273623 0 0 0 1 0 0 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15603534 1 0 0 0 0 1 0 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15293287 0 0 0 1 0 1 1 0 0 0 ... 0 0 0 0 0 0 0 0 0 0
stories/15285767 1 0 0 0 0 0 1 1 0 1 ... 0 0 0 0 0 0 0 0 0 0

4616 rows × 11216 columns

### Alternative bag-of-words features¶

I'll quickly review some things that I could be doing differently, but am not.

Many text retrieval systems perform stemming:

A stemmer for English, for example, should identify the string "cats" (and possibly "catlike", "catty" etc.) as based on the root "cat", and "stems", "stemmer", "stemming", "stemmed" as based on "stem". A stemming algorithm reduces the words "fishing", "fished", and "fisher" to the root word, "fish". On the other hand, "argue", "argued", "argues", "arguing", and "argus" reduce to the stem "argu" (illustrating the case where the stem is not itself a word or root) but "argument" and "arguments" reduce to the stem "argument".

Intuitively, stemming should improve the performance of a classifier when the number of training examples is small. For instance, if "cat" is a relevant word for a category, "cats" probably is too, and we'll collect better statistics for word occurence if we group them together. On the other hand, this assumption might not always be true: for instance, it could be that "CAT" bulldozers are what's relevant. Also, most stemmers do some violence to the text by committing some errors.

Another possible improvement would be to ignore certain words. For instance, there is little value in words that occur only once or a few times, since whether they appear or not in documents which are relevant or not is just a matter of chance. Words that occur very often (say "the") are also unlikely to be predictive and are frequently treated as stop words.

Some ML algorithms do poorly when they are confronted by a very large number of features, others do better. Logistic regression, the algorithm I use, holds up pretty well, particularly if it is predictions that we want as opposed to insights.

Sticking with the bag-of-words model, I could also weight words based on how often they occur in the title (So that The Global Fund to Fight AIDS, TB and Malaria: A Response to Global Threats, a Part of a Global Future would count the word "Global" three times.) I could also weight words less if they occur frequently in the corpus as well as normalize the length of the title vector. Put those together and I'd get a tf-idf vector.

The case for the tf-idf vector could be stronger if I was using whole documents, but my experience and reading of literature seems to indicate that these choices don't usually make a big difference in the performance of the classifier.

### Beyond bag-of-words¶

Another place I could be going is beyond bag-of-words, to features that are sensitive to the position and order of words.

One scourge of Hacker News is articles of the form "X is down"; it might make sense to build this in as a handcrafted feature, but asking an algorithm to find it is tricky because the number of possible multiple-word phrases expands exponentially as the number of words increases. The training samples thus get divided more and more finely, and it is hard to tell if correlations we see are real or just the result of luck.

People get small amounts of lift on classification tasks like this using features such as Word2Vec, but I am currently unimpressed. To do significally better than bag-of-words, we need something that models and understands language pretty well.

## Output labels¶

The training labels are 1 if an article is considered relevant, 0 if it is not. Here is a sample of the labels that the classifier is trained and tested on:

relevant title
story
stories/15496663 0 Rent is the answer
stories/15608169 1 Irken – A statically-typed Scheme with row pol...
stories/15541887 0 Has the Title Engineer Become Meaningless?
stories/15274926 0 The Asshole’s Guide to Product Validation: How...
stories/15388767 0 VR Is Exactly Where It Needs to Be
... ... ...
stories/15352624 0 Taking Privacy Seriously: Leaving Google Behind
stories/15279484 1 Tips for giving your first code reviews
stories/15284129 0 Scientific way to prioritize software developm...
stories/15342649 0 Notes from an Apocalypse

5771 rows × 2 columns

Note that our task is a bit unfair for two reasons:

1. Its not always possible to tell what an article is about from the title. Some titles are descriptive, others are not.
2. Sometimes I evaluate articles by looking at just the title, but often I read the article. My judgement on an article is not just based on relevance, but also on quality. There are many spammy websites full of tensorflow tutorials, whistlestop summaries of the data science literature stuffed with ads, etc. I vote them down.

If I were just trying to replicate my ability to look at a title and guess at relevance and I wanted to tune it up to maximum accuracy, I would change the task. I might create a "neutral" category and only judge documents on the basis of the title.

## The classifier¶

Fortunately, the classifier I use is good at learning probabilities. Thus, if some fraction of articles with "Tensorflow" in the title are irrelevant, it builds that into its probability estimate.

The classifier I use is the Logistic Regression classifier from scikit-learn with the default parameters. I've tried other parameters and found settings that perform worse, but none that perform markedly better.

Note the decision function looks like:

$$\beta_0+\beta_1x_1+\beta_2x_2+\cdots+\beta_mx_m = \beta_0+ \sum_{i=1}^m \beta_ix_i$$

where the $\beta$(s) are the learned coefficients and the $x$(s) are the inputs. Note that the $x$(s) are zero or one depending on the absence or presence of a token, so the output of the classifier is the sum of the weights for all of the words that appear in the title added to the intercept $\beta_0$ and the document is considered relevant if the sum is greater than zero and irrelevant if it is less.

Note there are other algorithms such as linear regression, linear support vector classifier, multinomial naive bayes, perceptron, et al. that train the same decision function but may choose different weights. These algorithms may generalize better or worse than logistic regression; in the little testing I have done these have not performed notably better in accuracy but have often performed much worse in terms of CPU time.

Negative weights, therefore, indicate words that are found in irrelevant titles, and positive weights indicate words found in relevant titles:

coefficient
index
go -1.384093
security -1.357270
things -1.088976
learn -1.074222
world -1.073974
unity -1.049862
website -1.008311
vs. -0.979719
digital -0.978315
right -0.888086
... ...
keras 1.386110
feedback 1.429219
conversational 1.430680
deep 1.449445
json 1.490234
gpus 1.508770
library 1.607861
pytorch 1.608896
python 1.671314
analyzing 1.749520

11216 rows × 1 columns

Adding up these weights produces a log-odds score, which can be converted to a probability with an inverse logit function. If the log-odds function is zero, the predicted probability is 0.5; the naive way to get predictions is to predict that the article is relevant if the log-odds is positive, and negative if it is zero.

prediction log-odds probability title
story
stories/15574717 1.0 0.257790 0.564093 Show HN: Hack to add search to remarkjs slides
stories/15286237 0.0 -2.728917 0.061288 Top Rated Code Editors for Developers
stories/15560193 0.0 -5.000396 0.006690 Are you really middle class? 1960s standard of living now affordable to very few
stories/15471121 0.0 -3.242301 0.037605 The Dystopia Next Door
stories/15521303 0.0 -2.163712 0.103057 Elementary OS My Dear Watson
stories/15468297 0.0 -0.297099 0.426267 The tf.data API [slides]
stories/15488340 0.0 -1.705732 0.153718 Terraform Elasticsearch AWS Module Released
stories/15335048 0.0 -3.425640 0.031504 ​ATO resolves 'intermittent issues' affecting its online services, again
stories/15298208 0.0 -2.162536 0.103166 Event Sourcing for the Internet of Things
stories/15331005 0.0 -1.690279 0.155739 Using Big Data to Solve Economic and Social Problems
... ... ... ... ...
stories/15635102 0.0 -1.019417 0.265141 PoC||GTFO 0x16 [pdf]
stories/15316694 0.0 -2.392001 0.083785 Remembering the Utils: Substitutions with Sed
stories/15596311 0.0 -3.173552 0.040173 How Philadelphia Fixed Parking Craters Using Tax Policy
stories/15281593 0.0 -3.278992 0.036299 Show HN: SoundBrake 2.0 – Headphone device alerts you to outside sounds
stories/15277914 0.0 -2.999032 0.047470 Linux Thinkpad Wiki
stories/15427022 0.0 -2.188245 0.100811 With Big Data Comes Big Responsibility
stories/15570022 0.0 -0.797042 0.310659 Show HN: Empathize – manage user conversations easily
stories/15326624 0.0 -2.426735 0.081157 Older versions of Reason not compatible with High Sierra

# But how well does it work, really?¶

For many reasons, it is tempting to evaluate performance with a single number. That's important for competitions on Kaggle and ImageNet, but less so in the real world.

As is the case with logistic regression, most classifiers return some kind of confidence value which can be handled with a varying cutoff point that lets us make a trade between getting fewer positive results with higher precision as opposed to more positive results with worse precision.

To evaluate the performance of the system, we need to split up the data set into a training set and a test set. For this experiment, I use a 80% train and 20% test split.

This curve illustrates the tradeoff: if I set a high confidence threshold, I am in the lower left corner. Clearly there is a range where I can get 20% or so of the wanted articles with a tiny fraction of unwanted articles. We can get around 60% of the wanted articles with a false positive rate of 20%, and 80% with a false positive around 50%.

Going to upper right, however, there is still a hard core of good articles that will be hard to get without tolerating feed which is mostly irrelevant. That's life. If I read Hacker News without any filter that's what I would get.

Practically one might be concerned with a particular operating point, or, in my case, I feel that I can look at a certain number of postings a day and want to make the most of that. Looking at the curve helps you make choices, but if you want to tweak the algorithm and know if it got better or worse, you still need to distill "quality" down to one number, and that number is the area under (the) curve for the receiver operating characteristic, or the ROC AUC.

For the plot above, the area is 0.76. The diagonal line on the plot represents the case of a classifier without predictive value, and corresponds to an AUC of 0.5.

It's not hard to make a plot that is that bad by making a bad model. For instance, if I use just 1% of the data for training (57 samples) I get a model that hasn't learned anything.

That's an important point, because it takes quite a few judgements to train a text classifier -- that's one reason why text classification hasn't become more widespread (and why Relevance Feedback hasn't set the world on fire.)

I think many people would expect to start getting good results with 5 or 10 judgements, but this system is doing poorly with 50. Real-world success, therefore, involves setting realistic expectations and gathering hundreds, if not thousands, of judgements.

# How many judgements does it take to make a good model?¶

That's a good question, and fortunately scikit-learn gives us the tools to answer it.

The technique is straightforward: I just compute the ROC curves using different amounts of training data. The green curve below is the one to look at, as it represents the AUC ROC for the test data. The red curve represents the AUC ROC for using the training data -- the results look a lot better when we use the training data because the model is overfitting; even though it is learning something relevant to the test data, it's learned how to cheat on the training data, finding words that can identify and classify most of the individual titles in the data set:

I don't know exactly how to map the ROC AUC to how satisified I would be with the output, but looking at the error bars, I'd imagine that I'd be happy with the results if I had 1200 training samples; maybe even 500. On the other hand, the AUC seems to be reaching an asymptope around 0.75 and it seems likely that I wouldn't get dramatically better results by adding more training data to this model.

I zoom in on the case of low numbers of training samples in order to get a sense of where learning starts:

The error bars seem to clearly be pulling away from the 50% mark when we have somewhere between 100 to 200 examples. Using 2% of the data for training (115 samples) the ROC curve is visibly pulling away from the diagonal:

The user's subjective experience is the real metric here, so if I look at the sorted predictions with 115 training samples, they really aren't bad:

prediction log-odds probability title
story
stories/15451601 1.0 0.934137 0.717914 An algebraic generalization for graph and tensor-based neural networks [pdf]
stories/15425829 1.0 0.880493 0.706924 Deep Learning Library 1.0 – Fast Neural Network Library
stories/15441782 1.0 0.795858 0.689088 Stanford Network Analysis Platform: Graph Mining Library and Datasets
stories/15629253 1.0 0.604679 0.646726 Show HN: PySchemes – A library for validating data structures in Python
stories/15374307 1.0 0.411127 0.601358 FastText: Library for efficient text classification and representation learning
stories/15558018 1.0 0.385377 0.595169 TimescaleDB: PostgreSQL made scalable for time-series data [pdf]
stories/15383148 1.0 0.294462 0.573088 Learning from Feedback: Evidence from New Ventures [pdf]
stories/15389287 1.0 0.232262 0.557806 Libact: Pool-Based Active Learning in Python
stories/15636730 1.0 0.218231 0.554342 Neural Discrete Representation Learning [pdf]
stories/15457181 1.0 0.148527 0.537064 Show HN: Scikit-plot – One-line functions for detailed visualizations – Python
... ... ... ... ...
stories/15607951 0.0 -3.895816 0.019922 Powering an Indoor Cycle Studio with Our Homegrown Technology, AKA, the Cyclers
stories/15423808 0.0 -3.902088 0.019800 Google, how old is the president?
stories/15493285 0.0 -3.910505 0.019637 Old Games, Remasters, and the Joy of Owning Your Work
stories/15480900 0.0 -3.960173 0.018703 When the plane takes off, why doesn’t the tail hit the runway?
stories/15394341 0.0 -3.984242 0.018267 The Gun Lobby Is Down to Its Last, Unconvincing Excuse
stories/15558175 0.0 -3.991387 0.018139 The universe shouldn’t exist, according to science
stories/15278500 0.0 -4.034383 0.017389 The Psychology of iPhone:A Neuromarketing Strategy, or an Overdose?
stories/15476574 0.0 -4.298847 0.013402 Bruno Latour, a veteran of the ‘science wars,’ has a new mission
stories/15284741 0.0 -4.546106 0.010497 'Bitcoin is a bubble,’ says the head of the world’s largest hedge fund
stories/15360671 0.0 -4.574913 0.010202 If you made a sphere of all the earth’s water, how big would it be?

5656 rows × 4 columns

Looking at the graphs, it seems there is a threshold between 50 and 100 training examples where the results go from "artificial stupidity" to "artificial intelligence": at 57 samples, the model only seems to have learned that it likes pdf files:

prediction log-odds probability title
story
stories/15283998 0.0 -0.335823 0.416824 AI-Produced Journalism â How WaPo's robo reporter published 850 articles
stories/15620794 0.0 -0.447031 0.390067 Multivariate Dependence Beyond Shannon Information [pdf]
stories/15278498 0.0 -0.660584 0.340608 Show HN: Peer review published journal articles
stories/15294773 0.0 -0.686719 0.334763 Traceroute and BGP AS Path Incongruities [pdf]
stories/15372054 0.0 -0.686719 0.334763 BIND 9.12 refactoring and performance improvements [pdf]
stories/15305161 0.0 -0.686719 0.334763 Zcash ceremony and audit [pdf]
stories/15354064 0.0 -0.689089 0.334236 Simple, Fast and Safe Manual Memory Management [pdf]
stories/15322398 0.0 -0.717672 0.327906 Mozilla's Internet health report [pdf]
stories/15341088 0.0 -0.723023 0.326728 OpenSMTPD, current state of affairs [pdf]
stories/15579474 0.0 -0.729435 0.325319 Non Serviam [1970, pdf]
... ... ... ... ...
stories/15588822 0.0 -3.581264 0.027086 Why is PyPy for python not as popular in the community?
stories/15278718 0.0 -3.618457 0.026123 The Problems with Redux: Are MobX and Realm Going to Put and End to It?
stories/15273416 0.0 -3.672061 0.024794 Google’s Tez payments app just went live. We tried it out to see how fast it is
stories/15319224 0.0 -3.679032 0.024626 Org-Mode Is One of the Most Reasonable Markup Language to Use for Text
stories/15339434 0.0 -3.687560 0.024422 A Notice by the Homeland Security (to collect social media info for immigrants)
stories/15315055 0.0 -3.835584 0.021133 Lynx identity manager is coming out of the garage. Want to take it for a spin?
stories/15289372 0.0 -3.841080 0.021019 What is the most confusing thing to you in Python?
stories/15461825 0.0 -3.915131 0.019548 Why is animation the medium of choice for startups to explain what they do?
stories/15601103 0.0 -4.265431 0.013851 The transition from mobile-first to AI-first is not only for Google but it’s

5714 rows × 4 columns

The consolation prize is that this model knows that it sucks (something good about logistic regression.) It never predicts that a posting has more than a 50% chance of being relevant, so if we set the decision threshold of 50%, it predicts that everything is irrelevant.

One ground rule of this analysis is that I'm only using information available from the Hacker News link, which includes the title, the submitter, and the url. We've seen that the title is fairly predictive.

I would have thought that I would have some 'friends' and 'foes' on HN, but it seems like the submitting user is not at all predictive of relevance.

To double check, here are some of the predictions.

prediction log-odds probability title
story
stories/15636853 0.0 -0.117590 0.470636 Resonance Audio: Multi-platform spatial audio at scale
stories/15346449 0.0 -0.257229 0.436045 Churn Prediction with Automatic ML
stories/15355051 0.0 -0.384499 0.405042 Acebusters opensourced own web app
stories/15528458 0.0 -0.512598 0.374585 Day 4 of 100 Days of VR: Going Through the Unity Space Shooter Tutorial III
stories/15528388 0.0 -0.512598 0.374585 Record proportion of people in employment are home workers (UK, 2014)
stories/15276421 0.0 -0.563047 0.362843 Show HN: TinyMCE and Evernote and RegEx Search
stories/15276386 0.0 -0.563047 0.362843 Creating a SaaS the wrong way
stories/15276417 0.0 -0.563047 0.362843 Optionsbleed bug in Apache HTTPD
stories/15633591 0.0 -0.570212 0.361188 Inventive Coding font in beta testing: CSS Mono
stories/15635154 0.0 -0.638260 0.345640 JUCE – Mobile Audio Quality Index
... ... ... ... ...
stories/15288654 0.0 -2.953646 0.049564 Lifelike Robots Possible with New “3x Stronger Than Human” Synthetic Soft Muscle
stories/15288703 0.0 -2.953646 0.049564 Show HN: Vincent – affordable, automatic meeting scheduling
stories/15288687 0.0 -2.953646 0.049564 German hackers step in to fix voting machines
stories/15358471 0.0 -2.998621 0.047488 Spending Time at India's First Mobile Congress
stories/15273464 0.0 -2.998621 0.047488 Is Social Media a Failure?
stories/15439743 0.0 -2.998621 0.047488 5 preload gotchas i wish i would knew in advance
stories/15273481 0.0 -2.998621 0.047488 Top Rated Code Editors for Developers
stories/15273338 0.0 -2.998621 0.047488 DSC with Infrastructure-As-Code and Azure Automation is a potent combination
stories/15577421 0.0 -2.998621 0.047488 Learning Depth-Three Neural Networks in Polynomial Time
stories/15273416 0.0 -2.998621 0.047488 Google’s Tez payments app just went live. We tried it out to see how fast it is

1155 rows × 4 columns

Those are pretty bad. In contrast, I get much better results using url hosts as a feature. (Like the badhosts mechanism used in the prefilter)

Looking at the RoC curve it seems that the hostname is highly predictive at the high-relevance and low-relevance sides of the curve, probably because there are a few sites that host a large number of articles which are balanced towards one direction or the other. Here are the top and bottom predictions:

prediction log-odds probability title
story
stories/15282816 1.0 0.269928 0.567075 One Leak Will Sink a Ship: WebRTC IP Address Leaks
stories/15553791 1.0 0.269928 0.567075 A Cost-Benefit Approach to Improving Browser Security
stories/15577421 1.0 0.269928 0.567075 Learning Depth-Three Neural Networks in Polynomial Time
stories/15607450 1.0 0.269928 0.567075 How intelligent are convolutional neural networks?
stories/15273210 1.0 0.269928 0.567075 Mathematics via Symmetry (2013)
stories/15372615 1.0 0.269928 0.567075 Infinitely many twin primes
stories/15488202 1.0 0.269928 0.567075 Generalization in Deep Learning [pdf]
stories/15414046 1.0 0.269928 0.567075 Interpretable Convolutional Neural Networks
stories/15626053 1.0 0.269928 0.567075 Simple and Scalable Predictive Uncertainty Estimation Using Deep Ensembles [pdf]
stories/15567373 0.0 -0.430549 0.393995 Can Vector Supercomputing Be Revived?
... ... ... ... ...
stories/15304986 0.0 -2.584873 0.070118 Project Jengo Strikes Its First Targets (and Looks for More)
stories/15404615 0.0 -2.626042 0.067481 Jayant Baliga's Quest to Make Silicon-Carbide Power Electronics Succeed
stories/15401254 0.0 -2.626042 0.067481 Three Advances Make Magnetic Tape More Than a Memory
stories/15400232 0.0 -2.626042 0.067481 China Demonstrates Quantum Encryption by Hosting a Video Call
stories/15438594 0.0 -2.626042 0.067481 GM Cruise Snaps Up Solid-State Lidar Pioneer Strobe Inc
stories/15384044 0.0 -2.626042 0.067481 AI to Help Power Grids Resist Disruptions
stories/15344022 0.0 -2.626042 0.067481 Drone with Event Camera Takes First Autonomous Flight
stories/15548852 0.0 -2.626042 0.067481 The Lure of a Fully Decentralized Internet
stories/15492303 0.0 -2.664825 0.065081 Turn your laptop into a portable whiteboard
stories/15454432 0.0 -2.664825 0.065081 Announcing Deep Learning, No Coding (DLNC)

1155 rows × 4 columns

Although the ROC AUC looks pretty good (better than I got for 117 training examples using words;) the top and bottom don't look so good to me.

Since we do seem to get some value out of the hostnames, what if we use the title words, submitters and hostnames to make one big model? The AUC is a touch better than what we get from using just the words (0.77 vs 0.74)

prediction log-odds probability title
story
stories/15528326 1.0 3.777827 0.977639 Study notes: Why deep and cheap learning works
stories/15527967 1.0 3.424605 0.968465 Learning Diverse Skills via Maximum Entropy Deep Reinforcement Learning
stories/15277179 1.0 3.032455 0.954019 Real-time object detection and deep learning and Python
stories/15451334 1.0 2.475431 0.922401 Mixed Precision Training for Deep Learning Models
stories/15438279 1.0 2.428966 0.919010 Neural Turing Machines (NTM): PyTorch Implementation
stories/15305774 1.0 2.409528 0.917551 Visualizing Dataflow Graphs of Deep Learning Models in TensorFlow
stories/15567545 1.0 2.288442 0.907915 A Deep Reinforcement Learning Framework for Crypto Financial Portfolios
stories/15461477 1.0 2.167837 0.897324 Show HN: Python library to automate your time management in Airtable and others
stories/15608012 1.0 1.943615 0.874749 DeepXplore: automated whitebox testing of deep learning systems
stories/15350422 1.0 1.874672 0.866998 Deep Learning in Finance [pdf]
... ... ... ... ...
stories/15307503 0.0 -5.208870 0.005438 5 Things You Should Look for in a Web Development Company
stories/15498010 0.0 -5.379586 0.004589 How Dopamine Tells Us Something Isn’t Worth the Wait
stories/15415392 0.0 -5.392626 0.004529 2017 Nobel Peace Prize to the International Campaign to Abolish Nuclear Weapons
stories/15294274 0.0 -5.452892 0.004266 Medical Device Security – Current State of Play
stories/15407336 0.0 -5.493184 0.004098 Google's Pixel Buds translation will change the world
stories/15504074 0.0 -5.662114 0.003463 Learn Go Programming – Monthly Recap #1
stories/15363571 0.0 -5.666140 0.003449 Nvidia CEO says Moore’s Law is dead and GPUs will replace CPUs
stories/15273129 0.0 -6.020664 0.002422 ‘Tez’: Google’s new digital payment app for India
stories/15288087 0.0 -6.024575 0.002413 Here Is the Pixel 2 in “Kinda Blue,” White, and Black – Starting at \$649
stories/15439686 0.0 -6.324011 0.001790 Security for People Who Don’t Want to Spend Much Time Thinking About Security

1155 rows × 4 columns

Next time I run my model (probably this evening) I will switch to the joint model since it seems to perform a bit better.

# Conclusion¶

Trained on roughly 5000 examples, a simple text classification model based on words in the title has proved effective for improving the relevance of a feed of articles from Hacker News. (See my last essay for my definition of "relevance".)

A model based on the submitter of the article was completely ineffective, and a model based on the hostname where the article is based was less effective than the word-based model. Adding both of those features improves relevance a bit on the ROC AUC (Reciever Operating Characteristic Area Under Curve) metric.

Although I might be able to do better by tweaking the features or using a different classifier than Logistic Regression, I am not inclined to mess with this model much more because a model based on the title and hyperlink is missing a large amount of information which could only be found on the target webpage. I'll be looking to that for future improvements, but that is going to involve beefing up the information harvesting system and probably some performance work on the machine learning side since the amount of text will increase greatly.

The one area where I did explore the parameter space was in the size of the training set. Particularly, this system seemed to learn nothing of value when given 57 training examples but it did visibly seem to learn when given 114 examples. Although the results improve when we use more training examples, there does seem to be a minimum number examples required to get meaningful results. Without some major change in the algorithm, therefore, classifiers that want to get across the "commercialization valley of death" will need to coax users to classify more documents than they might want to initially.