One of the approaches to graph drawing is application of so called force-directed algorithms. In its simplest form the idea is to layout the nodes on plane so that all edges in the graph have approximately equal length. This problem has very intuitive ... [Read more...]

While preparing for the new teaching semester I have created an implementation of NetLogo GenDrift P local in GNU R.The model works as follows. Initially a square grid having side size is randomly populated with n types of agen... [Read more...]

Recently I have read a nice post on ensuring that proper arguments are passed to a function using GNU R class system. However, I often need a more lightweight solution to repetitive function argument testing.The alternative idea is to test function arg... [Read more...]

Recently I have read a nice post on ensuring that proper arguments are passed to a function using GNU R class system. However, I often need a more lightweight solution to repetitive function argument testing.The alternative idea is to test function arguments against a specified pattern given in a ... [Read more...]

Recently I needed a simple example showing when application of regularization in regression is worthwhile. Here is the code I came up with (along with basic application of parallelization of code execution). Assume you have 60 observations and 50 expla... [Read more...]

Recently I have run an exam where the following question had risen many problems for students (here I give its shortened formulation). You are given the data generating process y = 10x + e, where e is error term. Fit linear regression using lm, ne... [Read more...]

I love using tikzDevice. When preparing LaTeX documents I switched to prepare all graphs in GNU R and then port them to TeX using tikzDevice. Recently I have moved to GNU R 3.0.0 and was shocked to find that this package is no longer available on CRAN.... [Read more...]

When talking about smoothing splines a simple point to start with is a continuous piecewise linear regression with fixed knots. I did not find any simple example showing how to estimate the it in GNU R so I have created a little snippet that does the j... [Read more...]

Recently I had several discussions about using for loops in GNU R and how they compare to *apply family in terms of speed. I have not seen a direct benchmark comparing them so I decided to execute one (warning: some of the code presented today tak... [Read more...]

Recently I have used hexadecimal numbers in GNU R. The way they are parsed surprised me and is inconsistent with Java. As R Language Definition pdf only briefly mentions hexadecimal numbers here is what I have found.First I have checked the following c... [Read more...]

In GNU R the simplest way to measure execution time of a piece code is to use system.time. However, sometimes I want to find out how many times some function can be executed in one second. This is especially useful when we want to compare function... [Read more...]

During holiday break I have decided to solve 9-puzzle, which is 3x3 variant of a well known 15-puzzle. The solution has proven to be a nice application of igraph package. Warning: this time the code takes a bit more tame than usual in my... [Read more...]

Recently I have been working with GNU R optimization routines a lot. Function optim has a nice trace option that allows to monitor optimization progress. Another standard function optimize has no such feature but it is pos... [Read more...]

Together with Mateusz Zawisza I have just published a new book in Polish on building predictive models in GNU R. It can be bought at Oficyna Wydawnicza SGH. The book presents complete examples of basic data mining processes.Although the book is in Poli... [Read more...]

Recently I played bridge with my friends. Being frustrated with several consecutive poor hand distributions we asked ourselves a question what is the probability of having a hand good enough for a small slam. A well known rule of thumb is that you need... [Read more...]

It has been just announced that during ESSA2013 conference I am planning to organize a special track on "Statistical analysis of simulation models". I hope to get some presentations using GNU R to promote it in social simulation community.It is obvious that GNU R excels in analysis of simulation ... [Read more...]

After my last post on Bayesian bootstrap I got a question why the sample from Dirichlet distribution is taken as weights for calculating mean in the procedure and not as weights used for sampling from the original data set. Actually this mistake i... [Read more...]

Bootstrapping is a very popular statistical technique. However, its Bayesian analogue proposed by Rubin (1981) is not very common. I was looking for an example of its implementation in GNU R and could not find one so I decided to write a snippet presen... [Read more...]

Recently I wanted to reproduce Figure 2 from Watts and Strogatz (1998). The task using igraph is simple but an interesting task was annotation of the resulting plot.Watts-Strogatz model generates graphs that have so called small-world ne... [Read more...]

Last week I have posted about using simulation metamodeling to verify results of analytical solution of the model. After posting it I realized that the solution presented there can be improved by using knowledge of simulation model struc... [Read more...]