R Tutorial: the non-linear equation solver

Need a numerical solution to simultaneous non-linear equations?  The nleqslv package is just what you’re looking for!  The coding required is minimal; just define the equations you want solved in a function, set some initial values, and let ‘er rip.

Here’s an example that uses the method of moments to estimate the parameters of a beta-binomial distribution.

Bump charts get renamed as SLOPEGRAPHS

Charlie Park has a nice post describing Tufte’s slopegraphs (old chart, new name).

Kaiser Fung likes these a lot; he’s been calling them Bump charts.

I introduce these to my undergrads when we discuss the paired t test.

Tip from kottke.org.
Update (16 July).  James Kierstead publishes an R implementation.

Better than pretty

Pretty R is a syntax formatter for R, it generates highlighted and properly indented R code suitable for including in an HTML document.  Better yet, all the R keywords are linked back to an online reference manual at inside-r.org!  Check it out.

# multiple comparison with aov 
 
s <- read.table("dogFoodSales.txt",header=T)
 
# fit the ANOVA model and perform post hoc test (Tukey's HSD)
 
print( summary( smodel <- aov(sales ~ location, data=s) ) )
print( TukeyHSD(smodel,"location", ordered=TRUE) )
 
# check residuals for normality
 
qqnorm(smodel$residuals)
qqline(smodel$residuals)
print(shapiro.test(smodel$residuals))
 
# check for homogeneity of variance
 
attach(s)
print(bartlett.test(sales ~ location))
 
# just in case, verify with nonparametric test
 
print(kruskal.test(sales ~ location))
 
detach(s)

Tip from the R Bloggers.