I found myself having to reverse logic in some code I wrote recently due to the wants of the client doing a 180. I had been using reject! to remove elements in an array, and realized that I now wanted to use select! - only there is no select!

I started to write:

arr = arr.select{|a| some.method.here }

when it occured to me that was a little clunky. I wanted select in place.

Here’s my version of it:

   1  class Array
   2    def select!(&block)
   3      selected = self.select(&block)
   4      if selected.size > 0
   5        replace(selected) 
   6      else
   7        nil
   8      end
   9    end
  10  end

   1  >> arr = ["Ren", "Easy-E", "Ice Cube", "DJ Yella", "Dr Dre"]
   2  # => ["Ren", "Easy-E", "Ice Cube", "DJ Yella", "Dr Dre"]  
   3  
   4  >> arr.select!{|a| a =~ /^D/ }
   5  # => ["DJ Yella", "Dr Dre"]  
   6  
   7  >> arr.select!{|a| a =~ /^J/ }
   8  # => nil  
   9  
  10  >> arr
  11  # => ["DJ Yella", "Dr Dre"]

I use this method to grab a webpage and then access it later. It’s useful if you’re trying to scrape a page, for example, and don’t want to keep hitting it over the network. Note that I use this as part of a class which initializes the variable @local_dir at instance creation.

   1  def get_local_or_remote(id, webpage_uri_format)
   2      html = ""
   3      if File.exists? "#{@local_dir}/#{id}.html"
   4        html = File.read("#{@local_dir}/#{id.html")
   5      else
   6        webpage_uri = if webpage_uri_format.match(/:id/)
   7          webpage_uri_format.gsub(":id", id)
   8        else
   9          webpage_uri_format
  10        end
  11  
  12        html = insist(:delay => 60) do
  13          Net::HTTP.get_response(URI.parse(webpage_uri)).body
  14        end
  15  
  16        stfile = File.new("#{@local_dir}/#{id}.html", "wb")
  17        stfile.puts(html)
  18        stfile.close
  19      end
  20  
  21      return html
  22    end

I find myself doing this often.

   1  >> data = Model.find_all_by_something("Something")
   2  # => [... results...]  
   3  
   4  >> File.open("#{RAILS_ROOT}/db/data/somethings.yml", "w") do |f|
   5   >     f.puts data.to_yaml
   6   >   end