I studied Ecology as an undergraduate, which meant I spent a lot of time gathering and analyzing field data. One of the basic tools we used to look for relationships in a large set of variables was correlation and scatterplot matrices. Each of these ... [Read more...]

I remember a few weeks ago, there was a challenge in the R-help list to make the prime symbol in R graphics. In LaTeX, we simply write $X'$ or $X^\prime$. R has a rough support for math expressions (see demo(plotmath)) and they are certainly unsatisfactory for LaTeX users. ... [Read more...]

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It is well-known that R has several graphics devices — either the screen devices (X11(), windows(), …) or the off-screen devices (pdf(), png(), …). We can query the default graphics device in options(): getOption('device') In a non-interactive session, the default device is pdf(). This is why Sweave has to create a file ... [Read more...]

new paper on the α-convex hull appeared in the Journal of Statistical Software today (http://www.jstatsoft.org/v34/i05/paper). The α-convex hull is an interesting problem which caught my attention long time ago but I didn’t know a solution then. R has a function chull() which can ... [Read more...]

e know the real distribution of the F statistic in linear models — it is a non-central F distribution. Under H0, we have a central F distribution. Given 1 – α, we can compute the probability of (correctly) rejecting H0. I created a simple demo to illustrate how the power changes as other parameters ... [Read more...]

mber Watkins gave me a suggestion on the animation for the ratio estimation, and I think this is a good topic for my animation package. I’ve finished writing the initial version of the function sample.ratio() for this package, which will appear in the version 1.1-2 a couple of ... [Read more...]

otivated by the excellent R package pgfSweave, I begin to notice the font families in my graphs when writing Sweave documents. The default font family for PDF graphs is Helvetica, which is, in most cases (I think), inconsistent with the LaTeX font styles. Some common font families are listed in ?... [Read more...]

Here are some (trivial) R tips in the course Stat 511. I’ll update this post till the semester is over. Formatting R Code Reading code is pain, but the well-formatted code might alleviate the pain a little bit. The function tidy.source() in the animation package can help us format ... [Read more...]

I have to admit that the previous post on Christmas is actually not much fun. Today I received another pResent from Yixuan which is more interesting: Basically the code deals with letter polygons (i.e. glyphs) and plot them with proper projections from 3D to 2D space: ## original code by ... [Read more...]

ince animation 1.0-9, we will be able to create a PDF document with an animation embedded in it; the function is saveLatex(), and its usage is similar to saveMovie() and saveSWF(): you pass an R expression for creating animations to this function, and this expression will be evaluated in the ... [Read more...]

oday Romain Francois posted an interesting topic in the R-help list, and you can read his blog post for more details: celebrating R commit #50000. 50000 is certainly not a small number; we do owe R core members a big “thank you” for their great efforts in this fantastic statistical language in ... [Read more...]

inlin Yan posted a cool (hot?) simulation of burning fire with R in the COS forum yesterday, which was indeed a warm welcome. I’m not sure whether our forum members will be scared by the “fire” under the title “Welcome to COS Forum”. The fire was mainly created by ... [Read more...]

Today Ruya Gokhan Kocer asked me how to use the R function identify() in off-screen graphics devices. Actually it’s pretty easy as long as we obtain the list returned by identify(pos = TRUE). For example, # open a windows device x11() x = rnorm(20) y = rnorm(20) plot(x, y) # identify 5 points ... [Read more...]