I know how to generate a random number between 1 and 2 :
def random return (1 + rand(2)) end
but let's say I would like to return 1 in 80% of the calls and 2 in 20% of the call... which library should I use ? ( I've seen a lot at http://raa.ruby-lang.org/ )
thanks for your suggestions
No doubt there are better ways but something like (rand(100) + 120)/100 should do it.
Colin
Well, perhaps something that reveals the intention better:
def usually_one rand < 0.80 ? 1 : 2 end
-Rob
Rob Biedenharn Rob@AgileConsultingLLC.com http://AgileConsultingLLC.com/ rab@GaslightSoftware.com http://GaslightSoftware.com/
I know how to generate a random number between 1 and 2 :
def random return (1 + rand(2))
No it doesn't actually. 1 + rand would be better, though it depends what you mean by *between* whether even that is correct.
end
but let's say I would like to return 1 in 80% of the calls and 2 in 20% of the call... which library should I use ? ( I've seen a lot at http://raa.ruby-lang.org/ )
No doubt there are better ways but something like (rand(100) + 120)/100 should do it.
Colin
Well, perhaps something that reveals the intention better:
def usually_one rand < 0.80 ? 1 : 2 end
Yes, much better. I suppose it is the old programmer in me instinctively avoiding floating point to save on processor time. A bit silly when everything has hardware floating point.
Colin
Although I prefer Rob's suggestion as a better example of self documented code; this is another alternative...
def usually_one [1,2,2,2,2][rand(5)] end
...there's many ways to skin a cat 
*ahem* of course.. this is the total opposite of what the OP asked
for, and returns 1 in 20% of the calls 
sorry for not paying attention.... oops!
def usually_one rand < 0.80 ? 1 : 2 end
Yes, much better. I suppose it is the old programmer in me instinctively avoiding floating point to save on processor time. A bit silly when everything has hardware floating point.
Although I prefer Rob's suggestion as a better example of self documented code; this is another alternative...
def usually_one [1,2,2,2,2][rand(5)] end
Ha! Vindicated
ruby-1.8.7-p302 > begin ruby-1.8.7-p302 > t=Time.now ruby-1.8.7-p302 ?> 1000000.times{(rand(100) + 120)/100} ruby-1.8.7-p302 ?> puts Time.now-t ruby-1.8.7-p302 ?> end 0.905431
ruby-1.8.7-p302 > begin ruby-1.8.7-p302 > t=Time.now ruby-1.8.7-p302 ?> 1000000.times{rand < 0.80 ? 1 : 2} ruby-1.8.7-p302 ?> puts Time.now-t ruby-1.8.7-p302 ?> end 1.712769
ruby-1.8.7-p302 > begin ruby-1.8.7-p302 > t=Time.now ruby-1.8.7-p302 ?> 1000000.times{ [1,2,2,2,2][rand(5)] } ruby-1.8.7-p302 ?> puts Time.now-t ruby-1.8.7-p302 ?> end 1.150481
...there's many ways to skin a cat
But how fast can you do it?
Colin
Ha! Vindicated
I expected to get different times, but to keep the proportions the same... but I get a little difference in order of speed:
begin
?> t=Time.now
1000000.times{(rand(100) + 120)/100} puts Time.now-t end
1.200484
begin
?> t=Time.now
1000000.times{rand < 0.80 ? 1 : 2} puts Time.now-t end
1.249109
begin
?> t=Time.now
1000000.times{[1,2,2,2,2][rand(5)]} puts Time.now-t end
1.498434
...there's many ways to skin a cat
But how fast can you do it?
A fair bit faster if I don't build the array in every loop 
x=[1,2,2,2,2]
=> [1, 2, 2, 2, 2]
begin
?> t=Time.now
1000000.times{x[rand(5)]} puts Time.now-t end
1.026202
OK, I admit defeat. I am using ruby 1.8.7 which may be the reason for the different ratios you are seeing (assuming you are using 1.9.2). Interestingly the benefit of your technique is even greater on 1.8.7, taking only 0.67 secs on my machine.
Colin
Nah! Who cares if it takes half-a-second or a second to select a million random numbers.... any of the methods are perfect for selecting one number.
Was a nice distraction from the recent run of posts...
OK, I admit defeat. the benefit of your technique is even greater on 1.8.7, taking only 0.67 secs on my machine.
Nah! Who cares if it takes half-a-second or a second to select a million random numbers.... any of the methods are perfect for selecting one number.
The OP might be doing some statistical simulation, so might need millions of values, but probably not.
Colin
def usually_one
rand < 0.80 ? 1 : 2
end
Yes, much better. I suppose it is the old programmer in me
instinctively avoiding floating point to save on processor time. A
bit silly when everything has hardware floating point.
Although I prefer Rob’s suggestion as a better example of self
documented code; this is another alternative…
def usually_one
[1,2,2,2,2][rand(5)]
end
Ha! Vindicated
ruby-1.8.7-p302 > begin
ruby-1.8.7-p302 > t=Time.now
ruby-1.8.7-p302 ?> 1000000.times{(rand(100) + 120)/100}
ruby-1.8.7-p302 ?> puts Time.now-t
ruby-1.8.7-p302 ?> end
0.905431
ruby-1.8.7-p302 > begin
ruby-1.8.7-p302 > t=Time.now
ruby-1.8.7-p302 ?> 1000000.times{rand < 0.80 ? 1 : 2}
ruby-1.8.7-p302 ?> puts Time.now-t
ruby-1.8.7-p302 ?> end
1.712769
ruby-1.8.7-p302 > begin
ruby-1.8.7-p302 > t=Time.now
ruby-1.8.7-p302 ?> 1000000.times{ [1,2,2,2,2][rand(5)] }
ruby-1.8.7-p302 ?> puts Time.now-t
ruby-1.8.7-p302 ?> end
1.150481
Here’s my number from within and outside IRB from Mac OS 10.6.6:
ruby-1.9.2-head :001 > begin
ruby-1.9.2-head :002 > t=Time.now
ruby-1.9.2-head :003?> 1000000.times{(rand(100) + 120)/100}
ruby-1.9.2-head :004?> puts Time.now-t
ruby-1.9.2-head :005?> end
from-irb: 0.16657 from-ruby-script: 0.159452
ruby-1.9.2-head :006 > begin
ruby-1.9.2-head :007 > t=Time.now
ruby-1.9.2-head :008?> 1000000.times{rand < 0.80 ? 1 : 2}
ruby-1.9.2-head :009?> puts Time.now-t
ruby-1.9.2-head :010?> end
from-irb: 0.280634 from-ruby-script: 0.150247
ruby-1.9.2-head :011 > begin
ruby-1.9.2-head :012 > t=Time.now
ruby-1.9.2-head :013?> 1000000.times{[1,2,2,2,2][rand(5)]}
ruby-1.9.2-head :014?> puts Time.now-t
ruby-1.9.2-head :015?> end
from-irb: 0.521992 from-ruby-script: 0.35944
-Conrad
>>> def usually_one >>> rand < 0.80 ? 1 : 2 >>> end >> >> Yes, much better. I suppose it is the old programmer in me >> instinctively avoiding floating point to save on processor time. A >> bit silly when everything has hardware floating point. > > Although I prefer Rob's suggestion as a better example of self > documented code; this is another alternative... > > def usually_one > [1,2,2,2,2][rand(5)] > end >
Ha! Vindicated
ruby-1.8.7-p302 > begin ruby-1.8.7-p302 > t=Time.now ruby-1.8.7-p302 ?> 1000000.times{(rand(100) + 120)/100} ruby-1.8.7-p302 ?> puts Time.now-t ruby-1.8.7-p302 ?> end 0.905431
ruby-1.8.7-p302 > begin ruby-1.8.7-p302 > t=Time.now ruby-1.8.7-p302 ?> 1000000.times{rand < 0.80 ? 1 : 2} ruby-1.8.7-p302 ?> puts Time.now-t ruby-1.8.7-p302 ?> end 1.712769
ruby-1.8.7-p302 > begin ruby-1.8.7-p302 > t=Time.now ruby-1.8.7-p302 ?> 1000000.times{ [1,2,2,2,2][rand(5)] } ruby-1.8.7-p302 ?> puts Time.now-t ruby-1.8.7-p302 ?> end 1.150481
Here's my number from within and outside IRB from Mac OS 10.6.6: ruby-1.9.2-head :001 > begin ruby-1.9.2-head :002 > t=Time.now ruby-1.9.2-head :003?> 1000000.times{(rand(100) + 120)/100} ruby-1.9.2-head :004?> puts Time.now-t ruby-1.9.2-head :005?> end from-irb: 0.16657 from-ruby-script: 0.159452
I think I need a new laptop.
Colin
I use this often:
class Uuid def self.uuid return rand( 18446744073709551615 ).to_s( 36 ).rjust( 13, '0' ) end end
Nice, simple process (assuming it works... I've not tried it), but I don't think it has much to do with the topic of this thread, and it's not likely to create a *real* UUID (RFC4122) is it?
This old thread discusses it a bit:
Colin Law wrote in post #987114:
But how fast can you do it?
Ooh, that's an evil tweak... (a minor diversion which is much more fun than what I was doing)
Lenovo T61p, Core2Duo, T9300, 2.5GHz, ruby 1.9.2-p0
= 0.253025
And for curiosity, my Ubuntu 10.10 VM on top of the same hardware:
= 0.323791
I don't think it makes a true UUID, but I've run it into the billions and never got a repeat. So, effectively, it acts like UUID.