From: Robert Klemme <bob.news@...>
Date: 2003-10-02T18:05:33+09:00
Subject: Re: Array and hash iteration questions


"Ben Giddings" <bg-rubytalk@infofiend.com> schrieb im Newsbeitrag
news:3F7B0BAC.7030305@infofiend.com...
> Robert Klemme wrote:
> > cases = Hash.new {|h,k| h[k] = [0, 0]}
>
> Ah.  I couldn't remember how to use the block form properly.  I'm
actually
> going to use:
>
> cases = Hash.new {|hash, key| hash[key] = Hash.new(0)}
>
> Because it will make some of the later stuff more clear like
>
> cases[case]['Number'] += 1
> cases[case]['Errors'] += 1 if arr[OFFSET] =~ /Error/

No need to use a Hash for this...

Number = 0
Errors = 1

cases[case][Number] += 1
cases[case][Errors] += 1 if arr[OFFSET] =~ /Error/

I might be a bit pricky, but storing the array ref saves one hash lookup.
It *can* affect performance if you have a large amount of cases...  (see
below; although the timing is dominated by the iteration here, you can see
that the array is faster)

counters = cases[case]
counters[Number] += 1
counters[Errors] += 1 if arr[OFFSET] =~ /Error/

You could as well do

cases[case].instance_eval do
  self[Number] += 1
  self[Errors] += 1 if arr[OFFSET] =~ /Error/
end

I'm getting carried away... :-)

> > cases.sort.each do |ca, counter|
> >   printf "%10s: %4d", ca, counter[0]
> >   printf " %4d", counter[1] if counter[1] > 0
> >   print "\n"
> > end
>
> Aha, I just assumed hash didn't have a sort method, because the concept
of
> a "sorted hash" seemed meaningless, but since it actually returns an
array
> containing [key, value] pairs, that's perfect!

It is!  Thanks to Matz's wisdom.

> Thanks Robert

You're welcome.

Kind regards

    robert


10:17:02 [ruby]: ruby -rprofile lookups.rb
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
 62.50    13.93     13.93        2  6962.50 11140.50  Integer#upto
 26.22    19.77      5.84   100001     0.06     0.06  Hash#[]
 11.28    22.28      2.51   100001     0.03     0.03  Array#[]
  0.07    22.30      0.01        1    15.00    15.00
Profiler__.start_profile
  0.00    22.30      0.00        2     0.00 11140.50  Object#test
  0.00    22.30      0.00        3     0.00     0.00  Module#method_added
  0.00    22.30      0.00        1     0.00 11171.00  Object#testArray
  0.00    22.30      0.00        1     0.00 22281.00  #toplevel
  0.00    22.30      0.00        1     0.00 11110.00  Object#testHash
10:17:25 [ruby]: cat lookups.rb


def test(coll)
  0.upto( 100000 ) do
    coll[2]
  end
end

def testHash
  test( { 0 => 0, 1 => 1, 2 => 2 } )
end

def testArray
  test( [0, 1, 2] )
end

testHash
testArray

10:18:15 [ruby]: