From: Robert Klemme <shortcutter@...>
Date: 2010-10-20T16:47:35+09:00
Subject: Re: Help missing something BASIC

On Wed, Oct 20, 2010 at 3:40 AM, Don Norcott <dnorcott@mts.net> wrote:
> This code is conceptually what I want to do with the nokogiri code below
> s1 = [1,2,3] ; s2 = [4,5,6]; s3 = [7,8,9]
> str = [s1,s2,s3]
> str.each do |itm|
>  puts "********"
>  puts " #{itm[2]}" Select middle item from each s1 , s2 ,s3
>  puts "*********"
> end
> Results as expected
> ********
>  3
> *********
> ********
>  6
> *********
> ********
>  9
> *********
>
> I have an html page with multiple <table>...</table> elements
> (equivalent to str above) and want to process each table (equivalent to
> s1, s2, s3) and extract one item <td[ class="itemNumbr ...> from the
> table (equivalent to extracting the middle element in any  of s1 s2 s3).
>
> I initially thought this was straight forward - but I am missing
> something very fundamental when I move the concept to Nokogiri objects
> ---------------------- NOKOGIRI CODE ----------------------
> require 'open-uri'
> require 'nokogiri'
>
> doc = Nokogiri::HTML(open("c:/RUBY_OUT.TXT"));   # file containing web
> page
> doc.xpath("//table[@class='result']").each do |node|   # select a table
>  puts "*************"
>  puts node.to_html        # as expected
>   puts node.xpath("//td[@class='itemNumbr']")  # 15 per each
>  puts "*************"
> end
> ---------------------- NOKOGIRI CODE ----------------------
>
> The output below dispays the table HTML as expected - but not itemnumbrs
> ***********
> <table ..................../table> for item 1
> <td class ="itemNumbr.....<b1> 1.</b>...../td>
> <td class ="itemNumbr.....<b1> 2.</b>...../td>
> ......
> <td class ="itemNumbr.....<b1> 15.</b>...../td>
> **********
> **********
> <table ..................../table> for item 2
> <td class ="itemNumbr.....<b1> 1.</b>...../td>
> <td class ="itemNumbr.....<b1> 2.</b>...../td>
> ......
> <td class ="itemNumbr.....<b1> 15.</b>...../td>
> **********
> **********
> <table ..................../table> for item 3
> <td class ="itemNumbr.....<b1> 1.</b>...../td>
> .......
>
> The tables are outputted as expected Tables with itemnumbr 1 to 15
> sequentially.
> The node.xpath("//td[@class='itemNumbr']") acts as if node contains all
> 15 tables but the output indicates otherwise.  I think node should
> always contain HTML for a single table only, but I appear to be wrong.
>
> Also if i put a subscript on the first xpath
> doc.xpath("//table[@class='result'][5]").each do |node|
> to ensure only one table is found, still get itemnumbrs for all 15 table
> elements
>
> WHAT AM I MISSING HERE

Please do not shout.  You are probably missing how XPath works.  With
the queries given by you above you will always get *all* td nodes with
class "itemNumbr" in the document.  You need a two level approach
using *relative* queries:

irb(main):004:0> html = "<body>" << (1..3).map {|i|
"<table><td>#{i}</td></table>"}.join(" ") << "</body>"
=> "<body><table><td>1</td></table> <table><td>2</td></table>
<table><td>3</td></table></body>"

irb(main):005:0> doc = Nokogiri.parse html
=> #<Nokogiri::XML::Document:0x8231e0c name="document"
children=[#<Nokogiri::XML::Element:0x8231b6c name="body"
children=[#<Nokogiri::XML::Element:0x82319e4 name="table"
children=[#<Nokogiri::XML::Element:0x823185c name="td"
children=[#<Nokogiri::XML::Text:0x82316d4 "1">]>]>,
#<Nokogiri::XML::Text:0x8231496 " ">,
#<Nokogiri::XML::Element:0x82313fc name="table"
children=[#<Nokogiri::XML::Element:0x8231274 name="td"
children=[#<Nokogiri::XML::Text:0x82310ec "2">]>]>,
#<Nokogiri::XML::Text:0x8230eae " ">,
#<Nokogiri::XML::Element:0x8230e14 name="table"
children=[#<Nokogiri::XML::Element:0x8230c8c name="td"
children=[#<Nokogiri::XML::Text:0x8230b04 "3">]>]>]>]>

irb(main):006:0> doc.xpath '//td'
=> [#<Nokogiri::XML::Element:0x823185c name="td"
children=[#<Nokogiri::XML::Text:0x82316d4 "1">]>,
#<Nokogiri::XML::Element:0x8231274 name="td"
children=[#<Nokogiri::XML::Text:0x82310ec "2">]>,
#<Nokogiri::XML::Element:0x8230c8c name="td"
children=[#<Nokogiri::XML::Text:0x8230b04 "3">]>]

irb(main):007:0> doc.xpath('//table').each do |tab|
irb(main):008:1* p tab, tab.xpath('td') # relative!
irb(main):009:1> puts '----'
irb(main):010:1> end
#<Nokogiri::XML::Element:0x82319e4 name="table"
children=[#<Nokogiri::XML::Element:0x823185c name="td"
children=[#<Nokogiri::XML::Text:0x82316d4 "1">]>]>
[#<Nokogiri::XML::Element:0x823185c name="td"
children=[#<Nokogiri::XML::Text:0x82316d4 "1">]>]
----
#<Nokogiri::XML::Element:0x82313fc name="table"
children=[#<Nokogiri::XML::Element:0x8231274 name="td"
children=[#<Nokogiri::XML::Text:0x82310ec "2">]>]>
[#<Nokogiri::XML::Element:0x8231274 name="td"
children=[#<Nokogiri::XML::Text:0x82310ec "2">]>]
----
#<Nokogiri::XML::Element:0x8230e14 name="table"
children=[#<Nokogiri::XML::Element:0x8230c8c name="td"
children=[#<Nokogiri::XML::Text:0x8230b04 "3">]>]>
[#<Nokogiri::XML::Element:0x8230c8c name="td"
children=[#<Nokogiri::XML::Text:0x8230b04 "3">]>]
----
=> 0

Cheers

robert


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