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Re: Java 8 Streams and Eratosthenes

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Am 05.06.2013 18:45, schrieb markspace:
> On 6/5/2013 12:09 AM, Sebastian wrote:
>>> With streams, you have to account for the fact that the previous sieve
>>> has already removed a lot of values. (I assume; I'm no expert on Java
>>> lambdas.) How do you even do that? I don't know.
>>
>> that's taken care of by the chaining of the filters. One problem with
>
> How does that actually work though? I'm not familiar with the details of
> filters.
>
> For example if you have a stream of integers:
>
> 1 2 3 4 5 6 7 8 9 10 11 12 13...
>
> And you sieve out all the even ones after the first:
>
> 1 2 3 5 7 9 11 13...
>
> And then you try to sieve out all the multiples of 3 after the first:
>
> 1 2 3 5 7 9 11 13 15...
> ^
> position '6'
>
> The position of the '6' in the sieve is shifted to be the actual number
> 9. I don't see how the sieve is going to work like that. It gets more
> obviously worse as you add more filters.
>
> 1 2 3 5 7 11 13 17 ...
>
> For example sieving '4' is going to remove 17 here, and that's not
> right, 17 is prime.
>
>
Well, yes, the algorithm doesn't work like that - it's not really a 
sieve, it's a version of trial division (cf. the Melissa E. O’Neil:
reference in one of my other posts) which checks the primality of x by
testing its divisibility by each of the primes less than x. There is
no actual crossing off or sieving out going on.

If you're interested in Java 8 stream filters, just get NetBeans or
IntelliJ Idea plus the JDK from http://jdk8.java.net/lambda/
and start experimenting.

-- Sebastian

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Java 8 Streams and Eratosthenes Sebastian <news@seyweiler.dyndns.org> - 2013-06-04 23:54 +0200
  Re: Java 8 Streams and Eratosthenes Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-06-04 19:35 -0300
    Re: Java 8 Streams and Eratosthenes Sebastian <news@seyweiler.dyndns.org> - 2013-06-05 09:03 +0200
      Re: Java 8 Streams and Eratosthenes Sebastian <news@seyweiler.dyndns.org> - 2013-06-05 09:44 +0200
        Re: Java 8 Streams and Eratosthenes Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-06-05 17:43 -0300
          Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) Sebastian <news@seyweiler.dyndns.org> - 2013-06-10 01:27 +0200
            Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-06-09 22:28 -0300
              Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) Sebastian <news@seyweiler.dyndns.org> - 2013-06-10 19:43 +0200
                Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) markspace <markspace@nospam.nospam> - 2013-06-10 13:18 -0700
                Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) Sebastian <news@seyweiler.dyndns.org> - 2013-06-11 23:27 +0200
                Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) Sebastian <news@seyweiler.dyndns.org> - 2013-06-12 10:32 +0200
                Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) Sebastian <news@seyweiler.dyndns.org> - 2013-06-12 14:37 +0200
                Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) markspace <markspace@nospam.nospam> - 2013-06-12 12:05 -0700
                Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) Sebastian <news@seyweiler.dyndns.org> - 2013-06-12 22:53 +0200
                Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) markspace <markspace@nospam.nospam> - 2013-06-15 15:18 -0700
                Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) Sebastian <news@seyweiler.dyndns.org> - 2013-06-16 22:52 +0200
                Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-06-16 21:56 -0300
                Re: Lazy primes with Java 8 (was Re: Java 8 Streams and Eratosthenes) Sebastian <news@seyweiler.dyndns.org> - 2013-06-18 23:18 +0200
  Re: Java 8 Streams and Eratosthenes markspace <markspace@nospam.nospam> - 2013-06-04 17:24 -0700
    Re: Java 8 Streams and Eratosthenes Sebastian <news@seyweiler.dyndns.org> - 2013-06-05 09:09 +0200
      Re: Java 8 Streams and Eratosthenes markspace <markspace@nospam.nospam> - 2013-06-05 09:45 -0700
        Re: Java 8 Streams and Eratosthenes Sebastian <news@seyweiler.dyndns.org> - 2013-06-05 21:32 +0200
    Re: Java 8 Streams and Eratosthenes Sebastian <news@seyweiler.dyndns.org> - 2013-06-05 09:47 +0200

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