find primes

findPrimes.R

##################################################################
# Brute force method for finding all the prime numbers between
# nMin and nMax
##################################################################

findPrimes <- function(nMin, nMax) {
    # make sure min number is larger than 1, and break if true
    if (nMin == 1) 
        stop("\n\n **** Error: Please ensure nMin is larger than 1 (nMin > 1) ****")
    
    # make sure nMax isnt too large!
    if (nMax > 1e+08) 
        stop("\n\n **** Error: nMax too large!!, try nMax < 1e8 ****")
    
    # create a test range going from nMin to nMax
    test.range = c(nMin:nMax)
    
    # create iterator it
    it <- 2
    
    # iterate through test.range looking for multiples of smaller numbers
    while (it < nMax) {
        if (it %in% test.range) {
            #test whether 'it' is in test.range
            test.range <- sort(c(it, test.range[test.range%%it != 0]))  #if yes, then remove multiples amd ensure 'it' is added to updated list. this ensures small primes remain in list.
        } else {
            test.range <- test.range[test.range%%it != 0]  #if no, then remove large multiples
        }
        it <- it + 1
    }
    test.range
} 



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# Usage 
#######################################

findPrimes(11,87)