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Just a reminder when working with arrays of objects generated with Active Record.

[Model.find(1), Model.find(2), Model.find(3)] -
  [Model.find(1)] != [Model.find(2), Model.find(3)]

This does not behave as you would expect, because array subtraction compares elements on their object ids. Each find generates a new object, with a new id, so subtraction does not work. To get the behavior desired, do this instead:

to_be_removed = [Model.find(1)].map{|m| m.id}
[Model.find(1), Model.find(2), Model.find(3)].
  delete_if{|m| to_be_removed.include?(m.id)}

It’s not as beautiful, but it gets the job done.

I was really on a roll there for a while, right? A gem of a post every day or so, presentations at meetings, reading on scheme and now, I’m nowhere to be found. Well, please allow me to explain. It goes like this: got new job, quit old job, working both jobs for two weeks until finished with my final two weeks.

So yes, working two jobs is keeping my quite busy right now, leaving very little time for any decent posting. Wait until next week, when I’ll once again make you privy to the thoughts bubbling around in my head.

In the meantime, I’ll leave you with a nice unordered list of what’s been catching my eye:

• Camping is awesome.
• Zed Shaw and his Mongrel project rock!
• I want to build a proxy server in ruby using mongrel and mongrel plugins but don’t know when I’ll have time.
• I want a piece of software that will scan and parse weather, news headlines, and my top rss feeds, placing them into a video file that I can watch on my iPod.
• Java will probably move into the same category as VB in my about page.

You can look look forward to (or know to avoid) posts on these topics as soon as I’m able to return.

I read an article a few years ago, I believe in Guitar World, written by famed Phish guitarist Trey Anastasio. In it, he explained that one of the keys to being great at guitar is to know how to get to ‘C’ from any other note on the fretboard. Once this is known, he explains, this knowledge can be transferred to every other key.

So what does this have to do with programming? A lot I believe. Read the rest of this entry »

Oh ruby, you make my job so simple. I need a class method you’re lacking, and you just let me add it to you.

class Array
  def map_with_index(procedure=null)
    result = []
    if block_given?
      each_with_index {|item, i| result[i] = yield(item, i) }
    elsif procedure
      each_with_index {|item, i| result[i] = procedure.call(item, i) }
    else
      result = self
    end
    return result
  end
  alias :collect_with_index :map_with_index
end

[1, 2, 3, 4].map_with_index {|elem, i| elem + i } => [1, 3, 5, 7]

See how easy that was?

Last night’s meeting was a smashing success. We had our largest turnout ever with what I think was 28 people. My presentation went very well, with only a few minor corrections coming from the illustrious David Black. For those of you following along via the web, I’ve updated the copy of the presentation available here to reflect those corrections. Moving past my accomplishments, Zed Shaw gave a highly informative presentation on the use of statistics to gauge performance. Also, Greg Brown talked about his reporting library Ruport, which looks very interesting. Needless to say, the meeting was amazing, and I hope to see you at the next one.

Tonight’s presentation on higher order procedures is now listed on the Presentations page to your right. I’ll be adding some practice exercises later, but feel free to check out what I have already.

Look ma, I made my own object! It doesn’t handle state that well, but at least it can be passed messages and told to do things.

def make_number(x)
  lambda do |op, *y|
    if op == '+'
      make_number(x + y[0])
    elsif op == '-'
      make_number(x - y[0])
    elsif op == 'val'
      x
    end
  end
end

my_num = make_number(5)         => <#Proc>
my_num.call('+', 7).call('val') => 12

In case you can’t tell, this object creation makes use of higher order procedures. The make number procedure returns the anonymous procedure created by lambda. This form of object creation is not terribly practical, but it sure is cool.

While working on the upcoming presentation, I came to the realization that I have never used Microsoft Powerpoint. Being a good dork, I decided that now was not the time to learn and instead set out to find presentation software that would allow me to post my presentation to the web. S5 to the rescue. S5 is a creation of Eric Meyer that runs on html, css, and javascript. It looks great, is easy to use, and your presentation can be viewed by anyone anywhere. Great work Eric!