R and Datetimes and stuff

You may have figured out at this point that these posts' primary purpose is so I don't have to figure out this stuff again if I stop using R for 6 months.

Anyway, if you've got some strings and you want dates, use
as.Date(x)


But if you want datetimes (i.e. don't want to lose the time component), use
as.POSIXct(x)


Also, subset is nice:
subset(dat1, (t > '2009-01-01') & (t < '2009-01-05'))


Create a frame:
#make up some data
x = seq(-2*pi, 2*pi, by = 0.05)
#create the frame
datx = data.frame(x=x)
#add another column
datx$sinx = sin(datx$x)
#show the columns
names(datx)
#gives: [1] "x" "sinx"

See also http://www.statmethods.net/input/datatypes.html for a nice brief intro to R's different structures.

ggplot2 is awesome

I like R, but R+ggplot2 is awesome.



library("ggplot2")
x = seq(-2*pi, 2*pi, by = 0.05)
x1 = x + rnorm(length(x))/10
qplot(x, sin(x1), color=rgb(abs(sin(x)),0,1), geom = c("point", "smooth"))

Requires that you
install.packages() ggplot2, of course.

I'm currently working through Getting started with qplot (pdf).

The R Project for Statistical Computing

I've been playing with The R Project for Statistical Computing. I quite like it.

Here's a few of the first things I did, just playing around:

x = seq(-pi, pi, by = 0.01)
plot(sin(x), col = rgb(abs(sin(x*3)), 0, 0), cex=.2+3*abs(sin(x)), pch=16)
points(cos(x), pch=16, cex=.5, col = rainbow(length(x)))

n = 10000
breaks = 100
plot_count = 5
cols = rainbow(plot_count)

plot(x = c(), xlim=c(-0,1), ylim=c(0,3), main = "distribution of random sums", xlab = "Sum of N random numbers between 0 and 1/N", ylab = "density")

runifrep = function(n, reps) {
 tot = 0;
 for (i in 1:reps) {
  tot = tot + runif(n)
 }
 tot/reps;
}
for (i in 1:plot_count) {
 a = hist(runifrep(n, i), breaks=breaks, plot=0)
 lines(y = a$density, x = a$mids, col = cols[i], pch=3, cex = .1, xlim=c(-4,4), lwd = 3)
}

Note that cex is symbol size, pch is symbol and lwd is line width. http://www.harding.edu/fmccown/R/#misc has a nice list of symbols.