Trouble with Pushing Arrays to Arrays

ruby-talk
1

Hello everyone! I'm having some trouble with pushing an array to another
array. Maybe this is an easy fix that I'm just not seeing? Here's my
code:

require 'nokogiri'
require 'open-uri'

url = 'C:\\users\\derek\\desktop\\Schedule2.html'
doc = Nokogiri::HTML(open(url))

raw_course_list = Array.new
temp = Array.new

doc.css("tr").each { |row| # Search through every row
     row.css("td").each { |column|
          temp.push(column.text.strip)
     }
     # puts temp.class #=> Array
     # puts temp.size #=> 20
     # puts temp[7] # E.g. => "Intro to Financial Accounting"
     raw_course_list.push(temp)
     # puts "raw_course_list[0]: " + raw_course_list[0].to_s # ****
Always returns the last temp pushed, not what should be at [0] (the
first array ever pushed) ****
     # print "raw_course_list.size: ", raw_course_list.size, "\n" #
Correctly increases +1 each push
     temp.clear
}

puts raw_course_list.each { |i| puts i.to_s} # **** Prints out line
after line of empty arrays ****

···

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2

And one last thing: As you can see from the commented out code, the temp
array is working as intended -- every time the row.css("td").each
completes, it's filled with data from all the column in the HTML... The
problem occurs (I'm guessing) when I push temp to raw_course_list.

···

--
Posted via http://www.ruby-forum.com/.

3

Hi --

Hello everyone! I'm having some trouble with pushing an array to another
array. Maybe this is an easy fix that I'm just not seeing? Here's my
code:

require 'nokogiri'
require 'open-uri'

url = 'C:\\users\\derek\\desktop\\Schedule2.html'
doc = Nokogiri::HTML(open(url))

raw_course_list = Array.new
temp = Array.new

doc.css("tr").each { |row| # Search through every row
    row.css("td").each { |column|
         temp.push(column.text.strip)
    }
    # puts temp.class #=> Array
    # puts temp.size #=> 20
    # puts temp[7] # E.g. => "Intro to Financial Accounting"
    raw_course_list.push(temp)
    # puts "raw_course_list[0]: " + raw_course_list[0].to_s # ****
Always returns the last temp pushed, not what should be at [0] (the
first array ever pushed) ****
    # print "raw_course_list.size: ", raw_course_list.size, "\n" #
Correctly increases +1 each push
    temp.clear
}

puts raw_course_list.each { |i| puts i.to_s} # **** Prints out line
after line of empty arrays ****

The problem is that you're reusing temp, and clearing it.

temp =
result =

%w{ one two three }.each do |word|
   temp.push(word)
   result.push(temp)
   temp.clear
end

p result # => [, , ]
p result.map {|obj| obj.object_id } # => [606420, 606420, 606420]

I end up with three copies of temp inside result, and temp is empty.

Try creating the temp array inside the loop, and not clearing it. Or
let Ruby do more of the work:

raw_course_list = doc.css("tr").map { |row|
   row.css("td").map { |column| column.text.strip }
}

(if I've got the logic right -- if not, tweak as needed :slight_smile:

David

···

On Sat, 17 Apr 2010, Derek Cannon wrote:

--
David A. Black
Senior Developer, Cyrus Innovation Inc.
THE COMPLEAT RUBYIST, Ruby training with Black/Brown/McAnally!
http://www.compleatrubyist.com

4

The problem is that you're reusing temp, and clearing it.

Doh! I knew it was something easy. The raw_course_list is pushing a
pointer to temp, not creating a copy of temp to push. Is this correct?

···

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5

raw_course_list = doc.css("tr").map { |row|
   row.css("td").map { |column| column.text.strip }
}

Also, this coding worked perfectly. It's very elegant; thanks! I had to
look up map in the API to fully understand what was going on there :slight_smile:

···

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6

Hi --

···

On Sat, 17 Apr 2010, Derek Cannon wrote:

The problem is that you're reusing temp, and clearing it.

Doh! I knew it was something easy. The raw_course_list is pushing a
pointer to temp, not creating a copy of temp to push. Is this correct?

Yes, essentially, though the more standard word in Ruby is
"reference".

David

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

THE Ruby training with Black/Brown/McAnally
     COMPLEAT Coming to Chicago area, June 18-19, 2010!
              RUBYIST http://www.compleatrubyist.com