snippet to surround a tag with “smart quotes” if it contains any odd characters. i.e. to display tags entered in a flickr-like style (space separated except inside quotes)

tag.gsub(/^/,'“').gsub(/$/,'”') if tag[0].match(/[^A-Za-z0-9\-_.]/)

The options.delete with the default looks mildly interesting. Just wanted to remember that.

def font_size_for_tag_cloud( total, lowest, highest, options={} )
 return nil if total.nil? or highest.nil? or lowest.nil?
 #
 # options
 maxf = options.delete( :max_font_size ) || 14
 minf = options.delete( :min_font_size ) || 11
 maxc = options.delete( :max_color ) || [ 0, 0, 0 ]
 minc = options.delete( :min_color ) || [ 156, 156, 156 ]
 hide_sizes = options.delete( :hide_sizes )
 hide_colours = options.delete( :hide_colours )
 #
 # function to work out rgb values
 def rgb_color( a, b, i, x)
  return nil if i <= 1 or x <= 1
  if a > b
   a-(Math.log(i)*(a-b)/Math.log(x)).floor
  else
   (Math.log(i)*(b-a)/Math.log(x)+a).floor
  end
 end
 #
 # work out colours
 c = []
 (0..2).each { |i| c << rgb_color( minc[i], maxc[i], total, highest ) || nil }
 colors = c.compact.empty? ? minc.join(',') : c.join(',')
 #
 # work out the font size
 spread = highest.to_f - lowest.to_f
 spread = 1.to_f if spread <= 0
 fontspread = maxf.to_f - minf.to_f
 fontstep = spread / fontspread
 size = ( minf + ( total.to_f / fontstep ) ).to_i
 size = maxf if size > maxf
 #
 # display the results
 size_txt = "font-size:#{ size.to_s }px;" unless hide_sizes
 color_txt = "color:rgb(#{ colors });" unless hide_colours
 return [ size_txt, color_txt ].join
end

//via:http://www.whatspop.com/blog/2005/12/my-coldfusion-tagging-enginelibrary.cfm

<cfset tags_list = " CaMELCaSE comma, 'singlequoted' <b>bold</b> ""doublequoted"" double double this should be over the limit now " />

<cfset amount = 10 />
<cfset length = 20 />

<cfset tags_list = trim(tags_list) />
<cfset tags_list = lcase(tags_list) />

<cfset tags_struct = structnew() />
<cfloop index="tag" list="#tags_list#" delimiters=" ">
<cfset tags_struct[tag] = "" />
</cfloop>
<cfset tags_list = structkeylist(tags_struct," ") />
<cfset tags_list = listsort(tags_list, "textnocase", "asc", " ") />

<cfif tags_list neq "">
<cfif listlen(tags_list," ") lte amount>
<cfset amount = listlen(tags_list," ") />
</cfif>
<cfloop from="1" to="#amount#" index="tag">
/* Perform a database upload here */
<cfoutput>#htmleditformat(left(listgetat(tags_list,tag," "),length))#</cfoutput>
</cfloop>
<cfelse>
Sorry, you need to provide at least one tag
</cfif>

If we have the id for a post in postid and a limit of num and we want to find posts which share as many tags as possible with postid's post, the following SQL will get you there.

SELECT p.*, COUNT(pt2.post_id) AS count FROM posts p, posts_tags pt, tags t, posts_tags pt2 WHERE pt.post_id=#{postid} AND t.id = pt.tag_id AND pt2.post_id != pt.post_id AND pt2.tag_id=pt.tag_id AND p.id = pt2.post_id GROUP BY pt2.post_id ORDER BY count DESC LIMIT #{num};")

Yet more code from Snippets itself. When you narrow down posts by tags, I only want you to see tags which are shared by other posts which also have the same current tags. This is more difficult than it sounds, and requires use of a subselect:

SELECT *, COUNT(pt.post_id) AS count FROM posts_tags pt, tags t WHERE pt.post_id IN (SELECT pt.post_id FROM posts_tags pt, tags t WHERE pt.tag_id = t.id AND (t.name IN ('rails', 'ruby')) GROUP BY pt.post_id HAVING COUNT(pt.post_id)=2) AND t.id = pt.tag_id GROUP BY pt.tag_id ORDER BY count DESC;

The first query (inside the subselect) finds all post IDs for posts which definitely contain any of the current tags. The outer query finds all OTHER tags associated with these posts, therefore we find all (and the quantity of) the tags related to the input tags.

If you have three tables, 'posts', 'tags', and a join table 'posts_tags', and you wish to find all posts which are all associated with a number of different tags, you can use this SQL trick:

SELECT p.* FROM posts_tags pt, posts p, tags t WHERE pt.tag_id = t.id AND (t.name IN ('tag1', 'tag2', 'tag3')) AND p.id=pt.post_id GROUP BY p.id HAVING COUNT(p.id) = 3;

.. where 3 is the number of tags in total. In Ruby/Rails, if you have an array called 'tags' containing the tags, you could use this code:

@posts = Post.find_by_sql ("SELECT p.* FROM posts_tags pt, posts p, tags t WHERE pt.tag_id = t.id AND (t.name = '" + tags.uniq.join ('\' OR t.name=\'') + "') AND p.id=pt.post_id GROUP BY p.id HAVING COUNT(p.id) = " + tags.uniq.length.to_s)

This is how Snippets itself works. You can also add a p.user_id check to the HAVING operator to only find posts with certain tags by a certain user.