opts_chunk$set(fig.width = 5, fig.height = 5)

This is a minimal example which shows knitr working with HTML pages. See here for the output and here for the source.

Boring stuff as usual:

## a simple calculator
1 + 1

## [1] 2

## boring random numbers
set.seed(123)
rnorm(5)

## [1] -0.56048 -0.23018  1.55871  0.07051  0.12929

We can also produce plots (centered by the option fig.align='center'):

library(ggplot2)
plot(mpg ~ hp, mtcars)

qplot(hp, mpg, data = mtcars) + geom_smooth()

Errors, messages and warnings can be put into div's with different classes:

sqrt(-1)  # warning

## Warning: NaNs produced

## [1] NaN

message("knitr says hello to HTML!")

## knitr says hello to HTML!

1 + "a"  # mission impossible

## Error: non-numeric argument to binary operator

In the end, let's show off a 3D plot from the rgl package.

knit_hooks$set(rgl = hook_rgl)  # set up the hook first

if (require("rgl")) {
    demo("bivar", package = "rgl", echo = FALSE)
    par3d(zoom = 0.7)
}

## Loading required package: MASS

Well, everything seems to be working. Let's ask R what is the value of π? Of course it is 3.1416.