# Blog Archives

## Variance-Covariance Matrix in glm

July 20, 2007
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This is a small function Venables and Ripley provide in their MASS book. You don't need it anymore because vcov() has a method for the glm class. However, it is useful to see how to extract bits from a fitted model object.vcov.glm #return the variance-covariance matrix of a glm object #from p. 188 in Venables and Ripley....

## Visualizing Data

July 18, 2007
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Sometimes it is helpful to see the plots created from the example files within R libraries. Of course you can paste them directly into R, but this web page allows you to view the images within the context of the help files:R Graphical ManualsAlso, chec...

## Repeat elements of a vector

May 17, 2007
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Two methods. The first produces a vector, the second a one column matrix.x=1:10# Method 1rep(x,each=3)# Method 2matrix(t(matrix(x,length(x),3)))

## Convert image to matrix in R

May 17, 2007
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This is how to use the Pixmap library to read in an image as a matrix.> library(pixmap)# the next command may only work on Linux> system("convert foo.tiff foo.ppm")> img To get info on your new object: > str(img)Although included in the previous output, the size of the image can be extracted by:>[email protected] to extract the red channel...

## Calculate turning angles and step lengths from location data

May 16, 2007
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anglefun <- function(xx,yy,bearing=TRUE,as.deg=FALSE){ ## calculates the compass bearing of the line between two points ## xx and yy are the differences in x and y coordinates between two points ## Options: ## bearing = FALSE returns +/- pi inst...