From: David Alan Black <dblack@...>
Date: 2000-12-16T10:21:21+09:00
Subject: [ruby-talk:7367] Re: Ruby performance question

On Sat, 16 Dec 2000, Dave Thomas wrote:

> OK, this is tacky, and probably not worth it, but it knocks about 15%
> of the run times on my box, using an 80,000 line input file with 6
> key/value pairs per line. The idea is simply to avoid creating the
> intermediate object that contains a single key-value which is then
> split across the '='. Instead, we assume the input is well-formed and
> split into the final strings directly.
> 
> 
>      h = Hash.new
> 
>      while line = gets
>        a = line.chomp!.tr!('=', ',').split(',')
>        0.step(a.size-2, 2) do |i|
>          h[a[i]] = a[i+1]

(Oh, for Array#to_h!  Wouldn't: "h = line.to_h" be nice?)

If the lines are guaranteed to be well-formed, you could also do:

    while line = gets
      record = line.chomp!.split(/[,=]/)
      h[record.shift] = record.shift until record.empty?
      h.clear
    end

which bypasses the tr! phase.  And seems to pick up a bit of time -- a
quick benchmarking of the three versions, on a file of 20000 lines
(all right, I'm impatient :-) with six key-value pairs per line, looks
like this:

      user     system      total        real
 13.200000   0.030000  13.230000 ( 13.225895)   # Eric
 11.200000   0.050000  11.250000 ( 11.242669)   # Dave
  9.870000   0.040000   9.910000 (  9.918286)   # David


I wanted to use the reverse/pop (instead of shift) technique that
Brian Feldman had suggested for interleaving, but I couldn't figure
out how to get at the key before the value.  


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav