# Monthly Archives: March 2013

## Barycentric interpolation: fast interpolation on arbitrary grids

March 6, 2013
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$Barycentric interpolation: fast interpolation on arbitrary grids$

Barycentric interpolation generalises linear interpolation to arbitrary dimensions. It is very fast although suboptimal if the function is smooth. You might now it as algorithm 21.7.1 in Numerical Recipes (Two-dimensional Interpolation on an Irregular Grid). Using package geometry it can be implemented in a few lines of code in R. Here’s a quick explanation of what

## Exporting plain, lattice, or ggplot graphics

March 6, 2013
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A blend between a basic scatterplot, lattice scatterplot and a ggplot In a recent post I compared the Cairo packages with the base package for exporting graphs. Matt Neilson was kind enough to share in...

## Times per second benchmark

March 5, 2013
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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...

## Le Monde puzzle [#810]

March 5, 2013
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The current puzzle is as follows: Take a board with seven holes and seeds. The game starts with one player putting the seeds on the holes as he or she wishes. The other player picks a seed wherever. Then, alternatively, each player picks a seed in a hole contiguous to the previous one. The loser

## Predicted correlations and portfolio optimization

March 5, 2013
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What effect do predicted correlations have when optimizing trades? Background A concern about optimization that is not one of “The top 7 portfolio optimization problems” is that correlations spike during a crisis which is when you most want optimization to work. This post looks at a small piece of that question.  It wonders if increasing predicted … Continue reading...

## Easily plotting grouped bars with ggplot #rstats

March 5, 2013
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Summary This tutorial shows how to create diagrams with grouped bar charts or dot plots with ggplot. The groups can also be displayed as facet grids. Importing the data from SPSS All following examples are based on an imported SPSS … Weiterlesen →

## Load Balanced Parallelization with snowfall

March 5, 2013
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For some reason, I didn't notice a few months ago the best way to perform a parallelized version of Lapply with package snowfall. We implemented the parallel version of function lapply with the function sfLapply, in the development of our pipeline p...

## Updating R from R (on Windows) – using the {installr} package

March 5, 2013
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Upgrading R on Windows is not easy. While the R FAQ offer guidelines, some users may prefer to simply run a command in order to upgrade their R to the latest version. That is what the new {installr} package is …Read more »

## Create an R package from a single R file with roxyPackage

March 5, 2013
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Documenting code can be a bit of a pain. Yet, the older (and wiser?) I get, the more I realise how important it is. When I was younger I said 'documentation is for people without talent'. Well, I am clearly loosing my talent, as I sometimes struggle to understand what I programmed years ago. Thus, anything that soothes the...

## Visualizing neural networks from the nnet package

March 4, 2013
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Neural networks have received a lot of attention for their abilities to ‘learn’ relationships among variables. They represent an innovative technique for model fitting that doesn’t rely on conventional assumptions necessary for standard models and they can also quite effectively handle multivariate response data. A neural network model is very similar to a non-linear regression