mages' blog

Data.table rocks! Data manipulation the fast way in R

I really should make it a habit of using data.table. The speed and simplicity of this R package are astonishing.

Here is a simple example: I have a data frame showing incremental claims development by line of business and origin year. Now I would like add a column with the cumulative claims position for each line of business and each origin year along the development years.

It's one line with data.table! Here it is:

myData[order(dev), cvalue:=cumsum(value), by=list(origin, lob)]

It is even easy to read! Notice also that I don't have to copy the data. The operator ':=' works by reference and is one of the reasons why data.table is so fast.


And it is getting even better. Suppose you want to get the latest claims development position for each line of business and origin year. Again, it is only one line:

Claims reserving in R: ChainLadder 0.1.5-4 released

Last week we released version 0.1.5-4 of the ChainLadder package on CRAN. The R package provides methods which are typically used in insurance claims reserving. If you are new to R or insurance check out my recent talk on Using R in Insurance.

The chain-ladder method which is a popular method in the insurance industry to forecast future claims payments gave the package its name. However, the ChainLadder package has many other reserving methods and models implemented as well, such as the bootstrap model demonstrated below. It is a great starting point to learn more about stochastic reserving.

Since we published version 0.1.5-2 in March 2012 additional functionality has been added to the package, see the change log, but in particular the vignette has come a long way.

Many thanks to my co-authors Dan Murphy and Wayne Zhang.

Simulating neurons or how to solve delay differential equations in R

I discussed earlier how the action potential of a neuron can be modelled via the Hodgkin-Huxely equations. Here I will present a simple model that describes how action potentials can be generated and propagated across neurons. The tricky bit here is that I use delay differential equations (DDE) to take into account the propagation time of the signal across the network.

My model is based on the paper: Epileptiform activity in a neocortical network: a mathematical model by F. Giannakopoulos, U. Bihler, C. Hauptmann and H. J. Luhmann. The article presents a flexible and efficient modelling framework for:

• large populations with arbitrary geometry
• different synaptic connections with individual dynamic characteristics
• cell specific axonal dynamics

Time for an old classic game: Moon-buggy

I discovered an old classic game of mine again: Moon-buggy by Jochen Voss, based on the even older Moon Patrol, which celebrates its 30th birthday his year.

googleVis 0.3.3 is released and on its way to CRAN

I am very grateful to all who provided feedback over the last two weeks and tested the previous versions 0.3.1 and 0.3.2, which were not released on CRAN.

So, what changed since version 0.3.2?

Not much, but plot.gvis didn't open a browser window when options(gvis.plot.tag) were not set to NULL, but the user explicitly called plot.gvis with tag NULL. Thanks to Sebastian Kranz for reporting this bug. Additionally the vignette has been updated and includes an extended section on knitr.

As usual, you can download the most recent version from our project site. It will take a few days before version 0.3.3 will be available on CRAN for all operating systems.