Ruby Shorthand

Justin.tv's web code is written in Ruby. I've found myself using the same collection idioms over and over, so I've abstracted several of them into a file called shorthand.rb.

Most of our web code consists of manipulating collections in one form or another, which is probably why all the shorthand methods are for that. I'm particular proud of my % operator, which I believe is a specialized mapcar in spirit. Without further ado, code!

module Enumerable
  def %(field)
    map {|o| o.send(field)}
  end
end

class Hash
  def keys_sorted_by_value(options = Hash.new, &block)
    limit = options[:limit] || size
    offset = options[:offset] || 0
    
    sorted = map.sort_by do |key, value|
      if block
        yield(key, value)
      else
        value
      end
    end
    
    sorted.reverse! if options[:reverse]
    
    sorted.map {|key, value| key}.slice(offset, limit) || Array.new
  end
  
  def hmap
    h = dup
    keys.each do |k|
      h[k] = yield h[k]
    end
    h
  end
  
  def to_params
    map {|k, v| "#{k}=#{CGI::escape v.to_s}"}.join("&")
  end
end


class Array
  def hash_by(field)
    h = Hash.new
    each {|o| h[o.send(field)] = o}
    h
  end
  
  def center_first
    centered = Array.new
    last_pushed = false
    each do |x|
      centered.push(x) unless last_pushed
      centered.unshift(x) if last_pushed
      last_pushed = !last_pushed
    end
    centered
  end
  
  def random_subset(n=size)
    shuffle.slice(0, n)
  end
  
  def shuffle
    sort_by { rand }
  end
  
  def divide
    evens = Array.new
    odds = Array.new
    each_with_index do |x, i|
      if i % 2 == 0
        evens << x
      else
        odds << x
      end
    end
    [evens, odds]
  end
  
  def remove!(item)
    reject! {|x| x == item}
  end
  
  def remove(item)
    reject {|x| x == item}
  end
end

Other coders: If you have your own idioms like these, I'd love to see them! Post them!