This is what I see when i think about higher education in this country today:

Remember the housing meltdown ? Tough to forget isn’t it. The formula for the housing boom and bust was simple. A lot of easy money being lent to buyers who couldn’t afford the money they were borrowing. That money was then spent on homes with the expectation that the price of the home would go up and it could easily be flipped or refinanced at a profit.  Who cares if you couldn’t afford the loan. As long as prices kept on going up, everyone was happy. And prices kept on going up. And as long as pricing kept on going up real estate agents kept on selling homes and finding money for buyers.

Until the easy money stopped.  When easy money stopped, buyers couldn’t sell. They couldn’t refinance.  First sales slowed, then prices started falling…

Robert Sedgewick has the slides for a talk, Algorithms for the Masses on his web site.

My favorite slide is the one titled “O-notation considered harmful” — Sedgewick observes that it’s more useful to say that the running time of an algortihm is ~aN^c (and back this up with actual evidence from running the algorithm) than to have a theorem that it’s O(N^c) (based on a model of computation that may or may not be true in practice).

The serious point of the talk, though, is that everyone should learn some computer science, preferably in the context of intellectually interesting real-world applications. This is what Sedgewick is doing in his Princeton course and in his book with Kevin Wayne, Algorithms, 4th edition, which I confess I have not read. There’s a Coursera course, in six-week parts, starting in August and November respectively. For a lot of…

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.

If you fire up your R console, type “??apply” and scroll down to the functions in the base package, you’ll see something like this:

Let’s examine each of those.

1. apply
Description: “Returns a vector or array or list of values obtained by applying a function to margins of an array or matrix.”

OK – we know about vectors/arrays and functions, but what are these “margins”? Simple: either the rows (1), the columns (2) or both (1:2). By “both”, we mean “apply the…

People who want to learn the very basics of R may find these videos made by some Berkeley grad students useful.