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.

Here’s a fun fact. NHL first round winners were 45-54 in shootouts in the regular season. First round losers were 63-43.  Here are the match ups (higher regular season point total first, shootout record in parentheses, winner in bold):

• Rangers (4-5)  vs. Ottawa (6-4)
• Bruins (9-3) vs. Capitals (4-4)
• Devils (12-4) vs. Panthers (6-11)
• Penguins (9-3) vs. Flyers (4-7)
• Canucks (8-7) vs. Kings (6-9)
• Blues (4-10) vs. Sharks (9-5)
• Blackhawks (7-7) vs. Coyotes (6-10)
• Predators (5-5) vs. Red Wings (9-3)

So, the team with the lower shootout win percentage won seven out of eight series. The team with the higher point total only won four out of eight (Rangers, Blues, and Predators), in part because good shootout records inflated some teams’ point totals. Why do we still have shootouts again?