Blog Archives

Coat of arms of Poland challenge

January 5, 2012
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Coat of arms of Poland challenge

Last week I have experimented with coloring map of Poland in national colors. Vaidotas Zemlys improved on my effort by adding colors to map of Lithuania and posted a challenge to also add coat of arms to the plot. This proved to be a nice exe...

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Color map of Poland for the New Year

December 31, 2011
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Color map of Poland for the New Year

To celebrate the New Year I decided to plot map of Poland in our national colors.It was not so difficult using maps  package. Here is the result:and the code I used to generate it:library(maps)x.mid <- function(x1, x2, y1, y2, y.mid) {&nbs...

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Programming traps when using "sample"

December 23, 2011
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Programming traps when using "sample"

Standard sample function works differently when it gets single element integer vector as opposed to longer vectors. This can lead to unexpected bugs in R code.Several times I had a problem with code similar to one given here:for (i in 1:4) {&...

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Optimal regularization for smoothing splines

December 16, 2011
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Optimal regularization for smoothing splines

In smooth.spline procedure one can use df or spar parameter to control smoothing level. Usually they are not set manually but recently I was asked a question which one of them is a better measure of regularizatio...

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Stability of classification trees

December 9, 2011
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Stability of classification trees

Classification trees are known to be unstable with respect to training data. Recently I have read an article on stability of classification trees by Briand et al. (2009). They propose a quantitative similarity measure between two trees. The method is i...

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Comparing model selection methods

December 2, 2011
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Comparing model selection methods

The standard textbook analysis of different model selection methods, like cross-validation or validation sample, focus on their ability to estimate in-sample, conditional or expected test error. However, the other interesting question is to compare the...

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Working with isTRUE

November 25, 2011
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Working with isTRUE

This week I was running computations transforming some input files into output files. The problem was that it was a repeated process. If new input files were generated or old ones were updated I needed to calculate new output files. The transformation ...

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randu dataset, part 2

November 19, 2011
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randu dataset, part 2

In my last post I have plotted randu dataset to show that all its points lie on 15 parallel planes. But I was not fully satified with the solution and decided to show this numerically.It can be done in four steps:identifying four points lying...

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Plotting randu dataset

November 18, 2011
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Plotting randu dataset

Recently I have stumbled on help description of randu data from datasets package. It contains pseudorandom numbers that are flawed. Help says that "In three dimensional displays it is evident that the triples fall on 15 paralle...

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Applying multiple functions to data frame

November 10, 2011
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Applying multiple functions to data frame

A very typical task in data analysis is calculation of summary statistics for each variable in data frame. Standard lapply or sapply functions work very nice for this but operate only on single function. The problem is that I o...

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