James:
I'm going to make a leap of faith here and guess that we're in agreement
on this one--it's just a difference in where we are in understanding the
language. I'm just learning it and need to run the profiler, debugger,
take timing measurements, and read lots of examples to fully understand
it still. I wouldn't peddle my (lack of) Ruby skills to any client at
this time, but it's by taking these steps that I will become a good Ruby
software developer. Others may be able to make the transition from a
developer who can make the code work to one who is actually good at it
(accurate, maintainable, resource appropriate code done quickly) without
taking these steps, but I cannot.
Premature Optimization....suggests the famous quote originating from
Tony Hoare and restated by Donald Knuth: "Premature optimization is the
root of all evil". I've always thought this quote has all too often led
software designers into serious mistakes because it has been applied to
a different problem domain to what was intended.
The full version of the quote is "We should forget about small
efficiencies, say about 97% of the time: premature optimization is the
root of all evil." and I agree with this. Its usually not worth spending
a lot of time micro-optimizing code before its obvious where the
performance bottlenecks are. But, conversely, when designing software at
a system level, performance issues should always be considered from the
beginning. A good software developer will do this automatically, having
developed a feel for where performance issues will cause problems. An
inexperienced developer will not bother, misguidedly believing that a
bit of fine tuning at a later stage will fix any problems.
Knowing the language well enough, will cause me as an experienced
software developer to automatically build the best code, while the
inexperienced developer will continue to write code that gives people
like me a well above average income
I first saw
that the array class mixed in enumerable and that I could use the to_a
call from there, but a quick check using -r profile showed that my
original call to split was a much quicker way to convert from a string
to an array.
This sounds like premature optimization. Remember, you start
worrying about speed when the code gets too slow. Not before.
James Edward Gray II
James:
I'm going to have to respectfully disagree.
Well, I'm pretty darn sure you are in the minority on that one:
But one doesn't want to suppress one's knowledge. When I write a
program, if I happen to know that, say:
puts a
will run faster than:
eval "puts #{97.chr}"
then I can't really be blamed for using that knowledge, just because
the knowledge pertains to speed.
In other words, I don't think that avoiding premature optimization
means that one should never knowingly take speed into account when
choosing what to put in one's code. In fact, I would find it really
difficult to do that, because I wouldn't know how to choose among the
various alternatives available in a way that paid no attention to
execution speed.
This isn't an argument in favor of premature optimization; rather, I'm
suggesting that having and using some rough-cut knowledge of execution
speed (as between, say, split and unpack, or something like that)
isn't premature Nor is it optimization; it's really melioration.
Solely for my own amusement, since I'm still trying teach myself Ruby...
File.open("./words").read.split.collect! {|x| x if x.length == 10 &&
x.split(//).uniq! == nil}.compact!.each {|x| puts x }
Mark:
Thanks for doing this way. I had thought about trying to read it in and
split it up, but didn't know how to do it as I've only read a bit of the
pikaxe book. On my two processor G5 with 4 gb of memory, your version
is about 30% slower than the fastest method above. 18.69 vs 12.52
seconds. I intend to look a bit closer at your code and see if I can
see another way to speed it up.
Gary:
Thanks for your input also. I saw the redundancy when William James
gave me input, but really don't fully understand arrays vs strings in
Ruby yet and also the differences in print vs puts and other types of
output. I'll read through pikaxe a bit more right now.
Others:
Any input as to why it runs slower inside the file block? Have I
overlooked something simple?
Solely for my own amusement, since I'm still trying teach myself Ruby...
File.open("./words").read.split.collect! {|x| x if x.length == 10 && x.split(//).uniq! == nil}.compact!.each {|x| puts x }
One detail here is the file handle is not being closed. A few alternatives
that close the file:
# open with block
File.open("./words"){|f| f.read.split.collect! {|x| x if x.length == 10 && x.split(//).uniq! == nil}.compact.each {|x| puts x } }
# File.read method
File.read("./words").split.collect! {|x| x if x.length == 10 && x.split(//).uniq! == nil}.compact.each {|x| puts x }
# IO.readlines method
IO.readlines("./words").collect! {|x| x if x.length == 11 && x.split(//).uniq! == nil}.compact.each {|x| puts x }
Note, used length 11 because readlines keeps linefeeds; also changed all to
non-bang form of compact, as compact! would return nil if it didn't do any work.
(I.e. if all words in the input satisfied the criteria, collect! would have returned
nil, and we'd have gotten a NoMethodError: undefined method `each' for nil:NilClass.)
Not measurably faster than the first one, but seems better and more
Ruby
like to me.
I'm curious why you see it so? Personally, seems less Ruby-like to me.
--Steve
Steve:
Let me be the first to say that I certainly don't understand Ruby idiom
yet, that's why I'm using the word seems in my earlier reply. I may
feel quite different about the newer code in a few days... I like it
better because it's more succinct as there're fewer intermediate steps
and because I can see what it's doing quite quickly. My code looks a
bit like that K&R C that I learned in the early 80s. You can even see
my OTB style and probably guess that I still use vi(m) :). I'd rather
learn the Ruby idiom and that's part of what I was asking here.
Learning that 'puts' doesn't throw the EOF as I was expecting, was an
important lesson and so was the rite of passage that Mr Wright pointed
out. The Ruby language feels good to me, and I'd like it to feel as
comfortable as C does to me, so thanks again for all the kind help.
Bill:
Thanks for adding a bit more to reading it all in and processing script.
I like code that's quite readable and will take that over code that's
faster but not so readable in any case where I can get away with it.
That said, I still really like the regex that checks to see if the
string is unique. No conversion to an array and no need to re-check the
size of it all so the current piece of code I like best is:
f= File.open("./words").each { |w|
puts w if w.size == 11 && w !~ /(.).*\1/
}
It's also the fastest that I've tested. I would, however, add a comment
to explain what the regex does so I wouldn't have to stare at it for a
minute or two to figure it out after a few months away.
Alan
!? How on earth does that work? Every time I think I've sort of
got the hang of regexp, they spring something new on me.
I was also going to ask why everyone was doing "split( // )" instead
of "split( '' )"?
- oooh, coffee's ready...
Cheers,
Benjohn
Benjohn:
A . matches any char except the \n, putting it in (), makes it save in
\1 each time it matches, the .* matches zero or more chars that's not a
\n, so if we try to match a string such as "profligate\n" the regex
would first look for (p).*\p, with the second p being anywhere in the
string then (r).*(r), etc. A string with a repeating set of letters
"wristwatch\n" matches (w)rist\w and returns a match. I highly
recommend O'reilly's "Mastering Regular Expressions", I've only read the
first edition, but it's an eye-opener (or maybe the opposite if you try
to read it in bed :))
A note for those following along in the DOS world, the dos string ends
\r\n and won't return the expected result as a matching DOS string will
need to be 12 long. This sacrifices portability for speed (I didn't
want to use chop after each gets).
As to split, I just used what I'm used to from perl. It's an empty
pattern and makes sense to me that way.
Alan
It isn't really premature optimization if you are dealing with a
known problem domain and you already have a reasonable
sense of the performance issues that you will face. It is
nonsensical to throw away the knowledge you've gained from past
experience in the matter.
But when crafting new software, where you don't have any
particular knowledge of the performance issues, it
makes more sense to get something working correctly and in
a timely manner than to make premature assumptions about the
bottlenecks.
···
On Mar 11, 2006, at 12:00 PM, Stephen Waits wrote:
Additionally, the "no premature optimization ideal" is often taken a little too far. I intentionally call it an "ideal". I work on video games. A good portion of our job is optimization. If we didn't do *some* premature optimization, we'd be in bad shape.
!? How on earth does that work? Every time I think I've sort of got the hang of regexp, they spring something new on me.
I was also going to ask why everyone was doing "split( // )" instead of "split( '' )"?
- oooh, coffee's ready...
Cheers,
Benjohn
I was going to ask why everyone is not doing
w.unpack("C*").uniq! == nil
which seems faster than split(//) but slower than /(.).*\1/
3.2s puts l if l !~ /(.).*\1/
3.6s puts l unless l.unpack("C*").uniq!
7.3s puts l if l.split(//).uniq.size == 11
perhaps I deal with C code to much, but unpack seems a better String -> array mechanism.
eric (rather new to ruby)
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This isn't an argument in favor of premature optimization; rather, I'm
suggesting that having and using some rough-cut knowledge of execution
speed (as between, say, split and unpack, or something like that)
isn't premature Nor is it optimization; it's really melioration.
David
Thanks David and others who stated what I wanted to say better than I
did. Again, I don't think James and I disagree. I concede that
premature optimization is not a good thing, but that's not what I was
trying to do here. I'm trying to understand Ruby to the level that I
understand C. To me that means I know exactly why I use every call,
every construct. When I'm able to do this, I'll know Ruby the way I
want to and I'll be able to use Ruby to accomplish non-trivial tasks.
Knowing to use a faster or more easily understood construct at the time
of coding is what one would expect any experience programmer to do.
Trying to optimze beyond that from the beginning, is silly and
wrong--just as James pointed out.
Yes, Robert, I assumed that the gets threw an EOFError when it found
EOF, I just haven't read and understood all I need to yet. I really
appreciate all the input on this thread. It's proved to me that the
Ruby community is everything good that is being said about it on the
web.
That said, using the block form is trivially slower, according to the
time calls that I'm making on my Mac, no matter which solution. I'm not
really concerned about that, and agree with Robert's statement above
about the block being preferred. To not use the block form would be a
prime example of premature optimization.
On Sunday 12 March 2006 08:44 am, dblack@wobblini.net wrote:
This isn't an argument in favor of premature optimization; rather, I'm
suggesting that having and using some rough-cut knowledge of execution
speed (as between, say, split and unpack, or something like that)
isn't premature Nor is it optimization; it's really melioration.
I'm not sure whether this question has been answered yet. It's probably slower because you do not close the file handle in your first version (more precisely, you close it only if there is an error, which doesn't happen the way you did it).
f = File.open("./words")
begin
...
rescue EOFError
f.close
end
If you wanted it to be equivalent with the block version "f.close" would have to go to an "ensure" section.
Generally he block form is preferred because it closes the file handle. Your first version didn't do that.
This is probably what I'd do
IO.foreach("wordlist") do |line|
line.scan /\b\w{11}\b/ do |word|
puts word unless /(.).*\1/ =~ word
end
end
The first regexp finds all words with length 11 and the second excludes all words that contain repeting characters. HTH
Kind regards
robert
···
Alan Burch <orotone@gmail.com> wrote:
Others:
Any input as to why it runs slower inside the file block? Have I
overlooked something simple?
