Re: sorting student papers



John H Palmieri wrote:
A silly question for a rainy Monday:

I am teaching a class with roughly 50 students in it. They have
quizzes and homework each week, and I end up alphabetizing these
papers before I return them to the students. Some of you may be in
similar situations. My question: what technique should I use to sort
the papers? (Or maybe: what techniques do you use to sort papers in
situations like this?)

Notice that I'm not talking about writing computer code to implement
Quick Sort or something like that -- I'm talking about shuffling
actual pieces of paper around. I also have good information about the
keys on which I'm sorting: I can see how they are distributed through
the alphabet, for example, so if I want to divide them into two
roughly equal stacks, I can make a good guess about how to do that.

For a class of your size or less, what I generally do is
start with a pile of papers on my desk and use insertion
sort to transfer them into another pile, usually in my lap.
The wrinkle is that I keep a finger in the pile in my lap,
essentially dividing it into two piles. The finger is
placed at the insertion part of the last paper inserted.

In algorithmic terms, I'm essentially keeping a pointer
into the list at the location of the last search and doing
a linear search to find the next insertion location. I've
been doing this for quite a while and always promise
myself that I'll do a proper analysis, but of course
while I'm grading and sorting, I always have more pressing
tasks, so the promise is continually unfulfilled.

As an aside, this is an exercise I sometimes use for
a data structures or algorithms class, something like
these:

1. You're grading placement tests. You and two other
students have 500 [insert some appropriate number here]
tests and have to alphabetize them. You have three
desks to work on and a big party to go to in 20
minutes. What strategy do you adopt?

2. You have a box full of broken spaghetti and have
to sort the pieces by length. What's the fastest
algorithm you can use to do the sorting?

I don't know how useful these sort of things are for
the students, but, hey, I'm tenured and can arrange
things for my own enjoyment :-)


Regards,

Rick

.

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    (sci.math)