求R中给定n的k个光滑数

Question

Need to find all the k-smooth numbers for a given n. I tried the following:

library(gmp)

S <- c(1:30)

test <- function(range, k){
  if(!isprime(k)==2){
    print("k should be a prime number")
  }
  else{
    for(i in range[1]:range[length(range)]){
      pf <- as.integer(factorize(i))
      if(max(pf) <= k){ 
        print(range[i]) 
      }
    }

  }
}

At the console: test(s, 11)

[1] 1
[1] 2
[1] 3
[1] 4
[1] 5
[1] 6
[1] 7
[1] 8
[1] 9
[1] 10
[1] 11
[1] 12
[1] 14
[1] 15
[1] 16
[1] 18
[1] 20
[1] 21
[1] 22
[1] 24
[1] 25
[1] 27
[1] 28
[1] 30


 *Warning message:
    In max(pf) : no non-missing arguments to max; returning -Inf*

I want to get rid of the warning. Please help! Is it a problem with the factorize() function returning bigz. changed it to as.integer(factorize(i)) ? Not able to understand the reason for the warning

Answer 1

The problem is

factorize(1)
# bigz(0)
length(factorize(1))
# [1] 0

That returns an empty vector. And when you take the max of an empty vector, you get that warning

max(numeric())
# [1] -Inf
# Warning message:
# In max(numeric()) : no non-missing arguments to max; returning -Inf

And you get there because

isprime(1)
# 0

so by the definition of isprime() 1 is not a prime number. So i'm not sure how you want to handle the number 1, but that is your problem.

Answer 2

The problem is with the first value in S.

as.integer(factorize(1)) produces integer(0) and max(integer(0)) produces that error.

You can fix it like so:

if (length(pf)!=0) {
   if(max(pf) <= k){
      print(range[i]) 
   }
}