CSCI E-168

Thanks everyone — panelists and students — for making yesterday evening’s event a success.

For those of you who couldn’t make it, here’s the design of the t-shirt I had made for the course:

If you come to one of our meetings on Jan. 8 or 16, you can pick one up (there are still a few in L and a few in XL).

The shirts were made by my good friends at The Red Seat, who design shirts and other goodies for Sox fans: Their merchandise uses no imagery licensed by MLB, so they’ve had to use a lot of creativity in their designs.

By the way, not everyone filled out the sheet, so I had to guess for the additional sizes. I think we ran out of the M’s. Sorry about that! But larger sizes are frequently ok in t-shirts . . .

I have posted a summary of the survey here:

http://e168f07.7fff.com/private/docs/

What do we know a lot about? HTML+Web apps, languages, and databases. In the chart, I put Advanced and Intermediate together and calculated their sum. The chart is ordered by that, and then the data is stacked for Advanced, Intermediate, and Beginner. There’s a second chart for what we don’t know about.

Next time I do this survey, I will be adding the following skill categories: JavaScript/Ajax/DHTML, Microsoft SQL Server, Python, J2EE/JavaEE, and XML/XSLT/XPATH.

Microsoft languages seem to be in decline. I was shocked that few students seem to do DB2 anymore (DB2 has its roots in the original SQL research by Codd). Few in the group have no experience with Java. Few have no knowledge of at least one database. Good.

Also, on the positive side, C is hanging in there, which is good because it promotes an understanding of machine organization.

Instant Messaging has significant penetration, with AOL Instant Messenger (AIM) still being the leading IM client, but not by much; Google’s GTalk is hard on its heals. About half of you are using Feed Aggregators for RSS, and Google Reader is in the lead there. I was surprised the so few people use Bloglines.

A significant majority of students have laptops, and Windows still reigns.

A majority of you think the course will be moderately difficulty; the others say it will be hard. On average, you believe that a reasonable number of hours for class preparation is 8 hours, and that the number of hours you will actually have to prepare is about the same. I also broke this average out by estimated difficulty, and the results were what I would expected: Those who think the course will be moderately difficulty think it will be about a 6 hour commitment outside of class, while those who guess it will be hard say 9 to 10 hours.

I will summarize the information about those who have expertise to share after I contact them.

If you have any additional observations, please post them here as comments. You will observe that the data doesn’t seem to add up in some cases: That’s because some people left blanks, and/or I was scoring this while my daughter was running around distracting me.

I may blog at some point about these results at my personal blog: A lot to think about!

Assignment 2, Question 12 is about the growth of the population of organisms in petri dishes. There was an error in one of the generation calculations for the example scenario. I replaced that bit with a somewhat longer description of the problem, with tables that show how the dishes array is calculated at each generation. I think this should be clarifying. So if you’re working on Question 12, make sure to get the newest version of the PDF.

Also, a student asked: May I alter the values in the dishes Array? The answer is: Yes. I think it can be done without overwriting the dishes Array — you would do it by duplicating the prior generation (dishes.dup) or by creating a new Array based on the old one (Array.new(dishes)). However, this might make the solution look a lot messier.

Oct. 8 and Nov. 12 are both Extension School holidays. And they’re both Mondays. And we have a section on Monday. Harvard buildings will be closed.

My tentative plan is to have on-line sections on Monday and Tuesday (i.e., Oct. 8, 9, Nov. 12, 13) at 7:35 PM. We would likely do this in instant messenger. I would also answer section questions by e-mail.

More on this later.

Folks,

I’m getting some reports that when you click “run” in the slides the embedded Ruby doesn’t work on some systems.

This feedback is very helpful. Thank you. For those of you who are having problems, I may hijack your laptop if you have it with you to observe what is happening.

At the very end of this post, a word or two on why you shouldn’t worry too much if the embedded Ruby isn’t working for you…

You may have noticed that some code fails when the irb checkbox is checked. This is because irb-style evaluation proceeds line-by-line, and if there is a statement or expression that works over multiple lines (example: do/end) then you don’t get any intermediate output, and the embedded irb gets confused. But I’ve added some code so that in most cases the checkbox will initially be set correctly.

How to reset JRuby if embedded scripts aren’t running:

1. First off, remember: for now, Firefox only.

2. At times, JRuby has to be re-loaded. To do this, go to the URL and delete the pound sign and everything following. In other words, if your URL says:

http://e168f07.7fff.com/private/lectures/E168-02.html#(36)

Change it to:

http://e168f07.7fff.com/private/lectures/E168-02.html

2. Press return

4. Then re-load by pressing control-R or by clicking the re-load button.

5. Then wait a bit before clicking for the next slide; JRuby is loading. Maybe 10 seconds. In theory, you shouldn’t have to wait, but there may be some subtle timing issues: I’m loading JRuby in a separate thread (or at least using JavaScript’s setTimeout feature).

6. Now click to the next slide. When you get to the first code example, trying clicking run.

7. If THAT isn’t working, let me know.

Two more things:

1. If you click “run” or click inside the textarea that holds the Ruby, you will have to click outside the Ruby code (i.e., on the slide) so that clicks go to the slide, rather than to the textarea. HTML Slidy (the framework I’m using to write the slides) has a yucky event structure and I have to intercept the events. It’s not worth going into, but you may find that advancing the slides is not working the way you want because the Ruby textarea is “owning” the vents.

2. And, finally, remember: You can always cut-and-paste examples right into irb! The examples are supposed to be illustrative. My hope in putting all of these together was that it would be illustrative in the pedagogical setting of the lectures and section: Having the Ruby run in your browser is a bonus: Great if it works, but there’s a clear work-around, and possibly one that will provide more learning: Try code in irb.