Try out The Climate Impact Sorting Challenge! A quick game I just made that teaches you about the climate impact of different kinds of food.

Sometimes it feels a bit silly when a simple statistical model has a fancy-sounding name. But it also feels good to drop the following in casual conversation: “Ah, then I recommend a Plackett-Luce model, a straightforward generalization of the Bradley–Terry model, you know”, when a friend wonders how they could model their, say, pinball championship dataset. Incidentally, in this post we’re going to model the result of the IFPA 18 World Pinball Championship using a Plackett-Luce model, implemented in Stan as a generalization of the Bradley–Terry model, you know.

I know neither who Bradley, Terry, Plackett, nor Luce were, but I know when their models could be useful:

This is just a post to brag about that the CopenhagenR useR group is alive and kicking, again.

After COVID-19, the group (like so many other meetups) was on hiatus for a couple of years and without an organizer. In 2023, I thought I would try starting it again and, while it took a little while, I’m happy that I got together five great meetups for the spring 2024 season! Here’s a little bit about what went down.

There are tons of well-known global indicators. We’ve all heard of gross domestic product, life expectancy, rate of literacy, etc. But, ever since I discovered pinballmap.com, possibly the world’s most comprehensive database of public pinball locations, I’ve been thinking about a potential new global indicator: Public Pinball Machines per Capita. Thanks to Pinball Map’s well-documented public API, this indicator is now a reality!

Here’s how this was put together (and just scroll to the bottom for a CSV file with this indicator for all countries).

Upon discovering that the tiny town I live in has a pinball arcade with over 40 tables (!), I got a bout of pinball fever. I fancy myself a fairly accomplished video game player, but was disappointed to discover that my ability to keep Mario alive didn’t translate to preventing the pinball from draining. Assuming I just needed a bit of practice, I downloaded a virtual version of Fish Tales — a fun, fishing-based table from 1992 — and began practicing. Here’s the data and quick analysis of how I improved over 100 games of Fish Tales.

(By the way, if you didn’t know, the hobbyist pinball emulation scene is amazing. Almost every real pinball table from the last 70 years has been painstakingly 3D-model by someone and is available completely for free, but completely not legally…)

Five years ago I started a new role and I suddenly found myself, a staunch R fan, having to code in Python on a daily basis. Working with data, most of my Python work involved using pandas, the Python data frame library, and initially I found it quite hard and clunky to use, being used to the silky smooth API of R’s tidyverse. And you know what? It still feels hard and clunky, even now, 5 years later!

But, what seems even harder, is explaining to “Python people” what they are missing out on. From their perspective, pandas is this fantastic tool that makes Data Science in Python possible. And it is a fantastic tool, don’t get me wrong, but if you, like me, end up in many “pandas is great, but…”-type discussions and are lacking clear examples to link to; here’s a somewhat typical example of a simple analysis, built from the ground up, that flows nicely in R and the tidyverse but that becomes clunky and complicated using Python and pandas.

Let’s first step through a short analysis of purchases using R and the tidyverse. After that we’ll see how the same solution using Python and pandas compares.

Now that I’ve got my hands on the source of the cake dataset I knew I had to attempt to bake the cake too. Here, the emphasis is on attempt, as there’s no way I would be able to actually replicate the elaborate and cake-scientifically rigorous recipe that Cook followed in her thesis. Skipping things like beating the eggs exactly “125 strokes with a rotary beater” or wrapping the grated chocolate “in waxed paper, while white wrapping paper was used for the other ingredients”, here’s my version of Cook’s Recipe C, the highest rated cake recipe in the thesis:

~~ Frances E. Cook's best chocolate cake ~~

- 112 g butter (at room temperature, not straight from the fridge!)
- 225 g sugar
- ½ teaspoon vanilla, extract or sugar.
- ¼ teaspoon salt
- 96 g eggs, beaten (that would be two small eggs)
- 57 g dark chocolate (regular dark chocolate, not the 85% masochistic kind)
- 122 g milk (that is, ½ a cup)
- 150 g wheat flour
- 2½ teaspoon baking powder

1. In a bowl mix together the butter, sugar, vanilla, and salt 
   using a hand or stand mixer.
2. Add the eggs and continue mixing for another minute.
3. Melt the chocolate in a water bath or in a microwave oven. 
   Add it to the bowl and mix until it's uniformly incorporated.
4. Add the milk and mix some more.
5. In a separate bowl combine the flour and the baking powder.
   Add it to the batter, while mixing, until it's all combined evenly.
6. To a "standard-sized" cake pan (around 22 cm/9 inches in diameter)
   add a coating of butter and flour to avoid cake stickage.
7. Add the batter to the pan and bake in the middle of the oven
   at 225°C (437°F) for 24 minutes.

Here’s now some notes, photos, and data on how the actual cake bake went down.

In statistics, there are a number of classic datasets that pop up in examples, tutorials, etc. There’s the iris dataset (just type iris in your nearest R prompt), the Palmer penguins (the modern iris alternative), the titanic dataset(s) (I hope you’re not a guy in 2nd or 3rd class!), etc. While looking for a dataset to illustrate a simple hierarchical model I stumbled upon another one: The cake dataset in the lme4 package which is described as containing “data on the breakage angle of chocolate cakes made with three different recipes and baked at six different temperatures [as] presented in Cook (1938)¹”. For me, this raised a lot of questions: Why measure the breakage angle of chocolate cakes? Why was this data collected? And what were the recipes?

I assumed the answers to my questions would be found in Cook (1938)¹ but, after a fair bit of flustered searching, I realized that this scholarly work, despite its obvious relevance to society, was nowhere to be found online. However, I managed to track down that there existed a hard copy at Iowa State University, accessible only to faculty staff.

The tl;dr: After receiving help from several kind people at Iowa State University, I received a scanned version of Frances E. Cook’s Master’s thesis, the source of the cake dataset. Here it is:

Cook, Frances E. (1938). Chocolate cake: I. Optimum baking temperature. (Master’s thesis, Iowa State College).

It contains it all, the background, the details, and the cake recipes! Here’s some more details on the cake dataset, how I got help finding its source, and, finally, the cake recipes.

If you know one thing about bubble sort, it’s that it’s a horrible sorting algorithm. But Bubble sort is great for one thing. Bubble sort has one good use case: Beer tasting. Let me explain:

I’ve now been in the industry long enough to know that meetings are often too long. No one likes to be in meetings, and the longer they are, the worse it is. Not only do I know most meetings are too long, but I also know exactly how long a meeting should be, at most! Let’s not delay it any further; here’s Rasmus’s maximum meeting length formula:

You can see that I’m confident about the correctness of this formula, as I’ve already branded it with my own name and rendered it in $\LaTeX$. If that’s not enough to convince you, let me break it down further: