R Notes

A few very basic R examples

Loading a plain CSV file into a vector

  myvector = read.csv(file="path_to_csv_file", header=FALSE)

• You may then access each of the individual records using myvector[row, column]
  • Access entire columns using myvector[,1], myvector[,2], ... myvector[,n]
  • Access entire rows using myvector[1,], myvector[2,], ... myvector[n,]

Scatterplot two columns of a vector

In this example, myvector has 4 columns and we want to plot the 3rd and 4th

  plot(myvector[,3], myvector[,4], main="This is the title of the plot")

Plot a simple histogram

  hist(myvector[,3])

• Also try plot(density(myvector[,3])) for a density-plot

Linear regression

  mymodel = lm(myvector[,3] ~ myvector[,4])
  summary(mymodel)

Squeeze multiple plots onto a page ( 4x4 in this example )

  par(cfrow = c(4,4))
  # or par(cfcol = c(4,4)) depending on whether you want row or column ordering
  plot(myvector[,3], myvector[,4])
  plot(myvector[,3], myvector[,4])
  plot(myvector[,3], myvector[,4])
  plot(myvector[,3], myvector[,4])

For loops

  for (i in 1:100) { do_something_useful }

A complete example

• Launch R, and then paste this into the shell:

  # Scott's quick R example
  par (mfrow=c(2,2), oma = c(0, 0, 2, 0), mar = c(5.1, 4.1, 2.1, 2.1)); 

  a = rnorm(1000)
  b = rnorm(1000)
  c = rlnorm(20000)
  d = rnorm(20000, mean=5, sd=20) 

  plot(a, b, main = "A vs B", xlab="x axis", ylab="y axis", pch=20, col="blue")
  plot(c, d, main = "C vs D", xlab="x axis", ylab="y axis", pch=".", col=palette(rainbow(50)))
  hist(a, main = "Histogram of A", col="darkgreen")
  plot(density(b), main = "Density plot of B", col="red") 

  mtext("This is an example that combines multiple plots on a single page", line=0.5, outer=TRUE)