A brief introduction to “apply” in R

At any R Q&A site, you’ll frequently see an exchange like this one:

Q: How can I use a loop to [...insert task here...] ?
A: Don’t. Use one of the apply functions.

So, what are these wondrous apply functions and how do they work? I think the best way to figure out anything in R is to learn by experimentation, using embarrassingly trivial data and functions.

R has a JSON package

Named rjson, appropriately. It’s quite basic just now, but contains methods for interconversion between R objects and JSON. Something like this:

library(rjson)
data <- list(a=1,b=2,c=3)
json <- toJSON(data)
json
[1] "{\"a\":1,\"b\":2,\"c\":3}"
cat(json, file="data.json")

Use cases? I wonder if RApache could be used to build an API that serves R data in JSON format?