From: Robert Klemme <bob.news@...>
Date: 2004-04-16T18:44:11+09:00
Subject: Re: Performance of Hash.inject


"George Ogata" <g_ogata@optushome.com.au> schrieb im Newsbeitrag
news:87y8owny24.fsf@optushome.com.au...
> "Daniel Sheppard" <daniels@pronto.com.au> writes:
>
> > I was doing some playing with some implementations for Hash#== and
ended
> > up with some very counterintuitive timings.
> >
> > I have four equals methods, and I would have expected their
performance
> > to run (from best to worst):
> >
> > directInject - stops evaluating == after first bad match, no
> > intermediate arrays
> > keysInject - as above, but must create keys array
> > directCollect - evaluated == for all items all the time, intermediate
> > array of results
> > keysCollect - as above, but must create keys array.
>
> Your *Inject methods don't actually quit early; they just stop
> evaluating the second expression once val is false.  An explicit break
> speeds up the quick-exit case considerably.
>
> > def directInject(hash1, hash2)
> >   hash1.size == hash2.size &&
> >     hash1.inject(true) { |val, kv| val && hash2[kv[0]] == kv[1] }
>       hash1.inject(true) { |val, kv| val or break; hash2[kv[0]] ==
kv[1] }
> > end
> > def keysInject(hash1, hash2)
> >   hash1.size == hash2.size &&
> >     hash1.keys.inject(true) { |val, k| val && hash1[k] == hash2[k] }
>       hash1.keys.inject(true) { |val, k| val or break; hash1[k] ==
hash2[k] }
> > end

I would not use inject in this case anyway.  I'd prefer returns for fast
exit:

def directInject(hash1, hash2)
  return false unless hash1.size == hash2.size
  hash1.each { |k, v| return false unless hash2[k] == v }
  true
end

> Unless you're using a really old ruby, though, Enumerable#all? should
> outperform all of the above.

You mean

def directInject(hash1, hash2)
  hash1.size == hash2.size and
    hash1.all? { |k, v| hash2[k] == v }
end

Yeah, that's even better.

    robert