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Generate a list of primes in R up to a certain number
What are elegant ways to find all prime numbers in a specified range in R language?
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3Is this question any different than this one? http://stackoverflow.com/questions/3789968/generate-a-list-of-primes-in-r-up-to-a-certain-number – Chase May 01 '11 at 13:21
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@Chase: The two differences are that it asks for a range and it asks for "elegant ways" – Henry May 01 '11 at 21:57
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Here is a one line example which works in a narrow range: it is particularly important that the bottom of the range is more than the square root of the top. There can also be memory issues for wide ranges.
library(matrixStats)
pRange <- function(a,b) which(!rowCounts(!outer(a:b,2:sqrt(b),FUN="%%")))+a-1
For example
> pRange(1e8, 1e8+1e3)
[1] 100000007 100000037 100000039 100000049 100000073 100000081 100000123
[8] 100000127 100000193 100000213 100000217 100000223 100000231 100000237
[15] 100000259 100000267 100000279 100000357 100000379 100000393 100000399
[22] 100000421 100000429 100000463 100000469 100000471 100000493 100000541
[29] 100000543 100000561 100000567 100000577 100000609 100000627 100000643
[36] 100000651 100000661 100000669 100000673 100000687 100000717 100000721
[43] 100000793 100000799 100000801 100000837 100000841 100000853 100000891
[50] 100000921 100000937 100000939 100000963 100000969
In many cases it would probably be quicker to better to use John's version of a sieve from the earlier question and drop the unwanted lower values.
