## Lucky Number Per7

I swear it was Perl 5 just a moment ago. I turned my back for all of 5 minutes ...

I don't need the new features, but I don't like boilerplate and I'm happy to accommodate those who seek progress. Harking back to lessons from the past, SysAdmins of a certain age may remember the venerable a2p program for converting awk scripts to perl and the horrendous (but working) code that it produced. We had one of those running in production less than 2 years ago until I finally decided to re-write it in Modern P…

## Enter the Matrix ... with PDL

We interrupt this k-Means broadcast to bring you an important message about threading (the PDL kind, not the Perl kind - darn those overloaded terms!)

### The Assignment

Take two vectors, x and y, and create a matrix C from a function of the values of each element pair, such that

$\Large&space;C_{ij}=\frac{1}{x_i-y_j}$

## k-Meansk-Means-er

As we take another lap around the k-Means race trace, the Porsche 914-2 and Volvo 142E are still neck and neck. This time we'll try a straight-forward normalisation that linearly scales all values to the range [0,1] and see if they still end up in the same cluster.

## Possibly the best k-means clustering ... in the world!

Short post this time because I got nerd-sniped looking at the data. The fun part is that you quickly move from thinking about how to get your results to trying to work out what they mean.

Forget why I started down this road. Right now, we are seeking the answer to Lewis Carol's famous question, How is a Porsche 914-2 like a Volvo 142E? (well, that's what it was in the first draft) A quick summary for those who have just joined us.

pdl> use PDL::IO::CSV ':all'
pdl> $cars = rcsv2D('mtcars_001.csv', [1 .. 11], {text2bad => 1, header => 1, debug => 1}); pdl> p$cars->dims
32 11


You got 32 11, right?

## PDL: Episode VI - a New Book

The title is clickbait. I ran short of time this week and am ~~recycling~~^Wconsolidating comments, replies and thoughts. Let's talk about Books!

I would love a new PDL Book. One that's completely different from the original to maximize the surface of engagement to a new audience. As a "sequel", It would have the advantage of being able to refer the reader to the first book for longer explanations and be able to jump right into how to solve significant problems. brian d foy has just finished his Mojolicious book, so I bet he's got loads of free time on his hands. (although I remember him in the middle of writing it in 2018, so you may have to wait a bit)