From: "David A. Black" <dblack@...>
Date: 2010-04-18T23:23:45+09:00
Subject: Re: Elegant Solution to a Seemingly Simple Problem?

Hi --

On Sun, 18 Apr 2010, Derek Cannon wrote:

>> There are lots of ways to identify more precisely which part of the HTML
>> you want, using CSS selectors. Most easily, if the rows are inside
>> <table id='courses'> then seomthing like 'table#courses tr' could do it.
>
> Since my original post, I've been playing around with the code some
> more. I made a new way of getting courses that automatically filters out
> "non-course" rows. The code is:
>
> table = doc.css("tr").collect { |row|
>  row.css(".dddefault").collect { |column|
>    column.text.strip
>  }
> }
>
> This way, "non-courses" appear as empty arrays. I still don't know how
> to neatly get rid of the empty arrays... I tried .compact! but that
> doesn't seem to work.
>
>> doc = Nokogiri::HTML(open(url))
>> raw_course_list = doc.css("tr").collect { |row|
>>  t_row = row.css("td").collect { |column| column.text.strip }
>>  t_row.insert(2, "") if (t_row[1] == "TBA")
>> }.reject{ |i| i.size != 4 }
>
> Excellent example, I think this is much better than what I had earlier.
> I guess I could now replace your reject with i.empty?, right?
>
> PS - I changed raw_course_list to table to make it more readable.

I think having the condition and the reject be the last things in the
code are going to make it hard to follow it later. I wouldn't rule out
doing something a tiny bit more procedural but maybe a little easier
to parse visually, like this:

   doc = Nokogiri::HTML(open(url))
   table = []
   doc.css("tr").each do |row|
     cells = row.css("td").map {|cell| cell.text.strip }
     next unless cells.size == 4
     next unless cells[1] == "TBA"
     cells.insert(2, "")
     table << cells
   end

You could also extract some methods, and end up with something like:

   table = doc.css("tr").
             select {|row| valid_row?(row)  }.
             map    {|row| prepare_row(row) }

(The above is all untested.)


David

-- 
David A. Black, Senior Developer, Cyrus Innovation Inc.

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