Tag: R

a non-riddle

Unless I missed a point in the last riddle from the Riddler, there is very little to say about it: Given N ocre balls, N aquamarine balls, and two urns, what is the optimal way to allocate the balls to the urns towards drawing an ocre ball with no urn being empty? Both my reasoning […]

CRAN does not validate R packages!

A friend called me the other day for advice on how to submit an R package to CRAN along with a proof his method was mathematically sound. I replied with some items of advice taken from my (limited) experience with submitting packages. And with the remark that CRAN would not validate the mathematical contents of […]

Le Monde puzzle [#1105]

Another token game as Le Monde mathematical puzzle: Archibald and Beatrix play with a pile of n>100 tokens, sequentially picking m tokens from the pile with m being a prime number [including m=1] or a multiple of 6, the winner taking the last tokens. If Beatrix knows n and proposes to Archibald to start, what […]

My Favorite data.table Feature

My favorite R data.table feature is the “by” grouping notation when combined with the := notation.
Let’s take a look at this powerful notation.

First, let’s build an example data.frame.

d <- wrapr::build_frame(

Le Monde puzzle [#1104]

A palindromic Le Monde mathematical puzzle: In a monetary system where all palindromic amounts between 1 and 10⁸ have a coin, find the numbers less than 10³ that cannot be paid with less than three coins. Find if 20,191,104 can be paid with two coins. Similarly, find if 11,042,019 can be paid with two or […]

another attempt at code golf

I had another lazy weekend go at code golf, trying to code in the most condensed way the following task. Provided with a square matrix A of positive integers, keep iterating the steps take the highest square 𝑥² in A. find the smallest adjacent neighbour 𝑛 replace x² with x and n with nx until […]

riddles on Egyptian fractions and Bernoulli factories

Two fairy different riddles on the weekend Riddler. The first one is (in fine) about Egyptian fractions: I understand the first one as Find the Egyptian fraction decomposition of 2 into 11 distinct unit fractions that maximises the smallest fraction. And which I cannot solve despite perusing this amazing webpage on Egyptian fractions and making […]

A precursor of ABC-Gibbs

Following our arXival of ABC-Gibbs, Dennis Prangle pointed out to us a 2016 paper by Athanasios Kousathanas, Christoph Leuenberger, Jonas Helfer, Mathieu Quinodoz, Matthieu Foll, and Daniel Wegmann, Likelihood-Free Inference in High-Dimensional Model, published in Genetics, Vol. 203, 893–904 in June 2016. This paper contains a version of ABC Gibbs where parameters are sequentially simulated […]