* ... in the same vector.
On Dec 3, 2015, at 10:48 AM, Boris Steipe <boris.ste...@utoronto.ca> wrote:
> It's very commendable that you try writing your own functions to learn R. Of
> course the function factorize() is in gmp, but that's beside the point.
>
> Your code looks messy - before asking your question you could have removed
> all these print statements. It gets further messed up because you posted in
> HTML. The logic is awkward. Instead of returning from the inside of an
> infinite loop in spaghetti code fashion, write your loop to test for your
> termination condition. Use "<-" and "=" consistently! Don't write return (),
> but keep parentheses attached to their functions. "if( isprime(n) ){
> return(n)}" is enough for your first test. DRY (Do not repeat yourself).
> Whenever you find yourself writing essentially the same code in different
> places of your function, your logic is almost always wrong (you have three
> different places where you append to your prime list).
>
> But, funny enough, that's not actually the source of your problem. The
> problem is: you are using the gmp function nextprime(), which - although it
> doesn't say so in it's help page - returns a big integer of class bigz.
>
> str(nextprime(2))
>
> The problem is you can't mix integers and big integers in the same list.
>
> c(nextprime(2), nextprime(3))
> c(27, nextprime(2), nextprime(3))
>
> So keep it all as plain integers:
> currentPrime = as.integer(nextprime(currentPrime))
>
> ... and it will work as expected.
> But do clean it up.
>
>
> B.
>
> PS:
> factorize(18)
> Big Integer ('bigz') object of length 3:
> [1] 2 3 3
>
> ...
>
>
> On Dec 3, 2015, at 6:42 AM, Kevin Wright <wrightkevin3...@gmail.com> wrote:
>
>> Hi,
>>
>> I am very new to 'R' and am trying to write an R function which returns the
>> prime factors of a given number(n)
>>
>> Unfortunately, the function only works for very small numbers, if for
>> example I pass 18 to the function
>> a mysteriously long vector is returned. I have not been able to find where
>> or why this is happening.
>> I know I've done something wrong. I've tried using debugging statements.
>> Sometimes the
>> currentPrime variable seems to become some sort of array?!
>>
>>
>> can you help?
>>
>>
>> library(gmp)
>>
>>
>> #passing 18 returns: 2 1 0 0 0 1 0 0 0 1 0 0 0 3 0 0 0 1 0 0 0 1 0 0 0 1 0
>> 0 0 3 0 0 0
>> # expected: 2 3 3
>> getPrimeFactors = function(n){
>> primeList <- c()
>>
>> if( isprime(n) ){
>> primeList <- append(primeList,n)
>> return (primeList)
>> }
>>
>> currentPrime <- 2
>>
>> while(TRUE){
>> # Check if input is divisible by the current prime
>> if(n %% currentPrime == 0){
>> cat(sprintf("the number %f is divisible by %f\n", n,
>> currentPrime))
>> n = n%/%currentPrime
>>
>> cat(sprintf("value of n is %f\n", n))
>>
>> cat(sprintf("current prime :%f\n", currentPrime))
>> primeList = append(primeList,currentPrime)
>> # print(c("list contents:", primeList))
>>
>>
>> currentPrime = 2
>>
>> if( isprime(n)){
>>
>> primeList = append(primeList, n)
>> return (primeList)
>>
>> }
>>
>> }
>> else{
>> cat(sprintf("the number %f is NOT divisible by %f\n", n,
>> currentPrime))
>> #cat(sprintf("current prime before is: %f\n", currentPrime))
>> #print(c("current prime before:", currentPrime))
>> currentPrime = nextprime(currentPrime)
>> #cat(sprintf("current prime after is: %f\n", currentPrime))
>> #print(c("current prime after:", currentPrime))
>>
>> }
>>
>>
>>
>> }
>>
>>
>>
>>
>> }
>>
>>
>>
>>
>>
>>
>> }
>>
>> [[alternative HTML version deleted]]
>>
>> ______________________________________________
>> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
______________________________________________
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
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