monkeypatch to Date to get difference to other date asstring with any or all of years,months,weeks,days. started out as codegolf...

ymd.rb

class Date
  # prev_week and next_week, add/remove 7 days * optarg
  ['prev_','next_'].each{|n|define_method(n+'week'){|w=1|send n+'day',7*w}}

  # other is Date to compare to
  # wants tells what to include in timediff. default is years,months,weeks,days
  # by default   returns <timediff> from <earlier> to <later>
  # if abs=true  returns <self> is <timediff> later|earlier than <other>
  def diff_str other, want="ymwd",abs=false
    return "Both dates are #{self}" if self==other
    if self<other
      t,f=self,other
      a,b=t,f
      fmt='%s is %s earlier than %s'
    else
      t,f=other,self
      a,b=t,f
      fmt='%s is %s later than %s'
    end
    parts=[]
    parts<<[0,'year']  if want[?y]
    parts<<[0,'month'] if want[?m]
    parts<<[0,'week']  if want[?w]
    parts<<[0,'day']   if want[?d]
    parts=parts.map{|c,n| 
      while t<f 
        c+=1
        t=t.send"next_#{n}"
      end
      c,t=c-1,t.send("prev_#{n}")if t>f
      [c,n+(c>1??s:'')]*' 'if c>0 }.compact*', '
    abs ? parts+" from #{a} to #{b}"
        : fmt%[self,parts,other]
  end
end