# Monthly Archives: March 2010

## Converting Siemens MOSAIC

March 21, 2010
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Siemens multi-slice EPI data may be collected as a "mosiac" image; i.e., all slices acquired in a single TR (repitition time) of a functional MRI run are stored in a single DICOM file.  The images are stored in an MxN array of images.  The function create3D() will try to guess the number of images embedded within the single DICOM...

## R: Add vertical line to a plot

March 21, 2010
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If you have a plot open and want to add a vertical line to it: abline(v=20) #Add vertical line at x=20

## The distribution of rho…

March 21, 2010
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There was a post here about obtaining non-standard p-values for testing the correlation coefficient. The R-library SuppDists deals with this problem efficiently. library(SuppDists) plot(function(x)dPearson(x,N=23,rho=0.7),-1,1,ylim=c(0,10),ylab="density") plot(function(x)dPearson(x,N=23,rho=0),-1,1,add=TRUE,col="steelblue") plot(function(x)dPearson(x,N=23,rho=-.2),-1,1,add=TRUE,col="green") plot(function(x)dPearson(x,N=23,rho=.9),-1,1,add=TRUE,col="red");grid() legend("topleft", col=c("black","steelblue","red","green"),lty=1, legend=c("rho=0.7","rho=0","rho=-.2","rho=.9"))</pre> This is how it looks like, Now, let’s construct a table of critical values for some arbitrary or not significance levels. q=c(.025,.05,.075,.1,.15,.2) xtabs(qPearson(p=q, N=23, rho

## My Experience at ACM Data Mining Camp #DMcamp

March 21, 2010
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My parents and I made plans to visit San Jose and Saratoga on my grandmother’s birthday, March 19, since that is where she grew up. I randomly saw someone tweet about the ACM Data Mining Camp unconference that happened to be the next day, March 20, only a couple of miles from our hotel in Santa Clara. This was...

## R: Geometric mean

March 21, 2010
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gm(x) But this requires package heR.Misc so you might as well just use: exp(mean(log(x)))

## Returns on Easter week and one week after

March 21, 2010
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Inspired by CXO group report, I did a rerun of the same strategy on my data. Easter’s dates can be find at wikipedia. Overall, my results are similar to CXO group’s results. In the graph below, I plotted daily returns on Easter week (Monday to Thursday) from 1982 to 2009. I prefer this way of showing

## R annoyances

March 20, 2010
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Readers returning to our blog will know that Win-Vector LLC is fairly “pro-R.” You can take that to mean “in favor or R” or “professionally using R” (both statements are true). Some days we really don’t feel that way. Consider the following snippet of R code where we create a list with a single element Related posts:

March 20, 2010
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rm(list = ls())

## Package Releases

March 20, 2010
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I just put a new version of the XML package on the Omegahat repository. There is a new version of the RKML package which handles large datasets much more rapidly. Also, I put a new package named RJSCanvasDevice which implements and R graphics device that creates JavaScript code that can be subsequently display on a

## R: Backwards for loop

March 20, 2010
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for (i in 10:1) { print(i) } As easy as that.