On 29/01/2014 11:32 AM, Supriya Jain wrote:
Hi, I notice the following from a "for" loop in R, which seems strange to me:When I do this: ------- first <- 0 nstep <- 10 N <- 14 while(first < N) { print("-------> ") last <- first + nstep if(last > N) last <- N #start <- first+2 for(i in (first+2):last) # line 11 print(sprintf("i: %d; last: %d", i, last)) first <- first + nstep } # end of while loop ------- the output is as expected: [1] "-------> " [1] "i: 2; last: 10" [1] "i: 3; last: 10" [1] "i: 4; last: 10" [1] "i: 5; last: 10" [1] "i: 6; last: 10" [1] "i: 7; last: 10" [1] "i: 8; last: 10" [1] "i: 9; last: 10" [1] "i: 10; last: 10" [1] "-------> " [1] "i: 12; last: 14" [1] "i: 13; last: 14" [1] "i: 14; last: 14" but, if, on line 11 in code, I forget to enclose first+2 in parenthesis, that is, do: for(i in first+2:last) the output from the second iteration is very non-intuitive: [1] "-------> " [1] "i: 2; last: 10" [1] "i: 3; last: 10" [1] "i: 4; last: 10" [1] "i: 5; last: 10" [1] "i: 6; last: 10" [1] "i: 7; last: 10" [1] "i: 8; last: 10" [1] "i: 9; last: 10" [1] "i: 10; last: 10" [1] "-------> " [1] "i: 12; last: 14" [1] "i: 13; last: 14" [1] "i: 14; last: 14" [1] "i: 15; last: 14" [1] "i: 16; last: 14" [1] "i: 17; last: 14" [1] "i: 18; last: 14" [1] "i: 19; last: 14" [1] "i: 20; last: 14" [1] "i: 21; last: 14" [1] "i: 22; last: 14" [1] "i: 23; last: 14" [1] "i: 24; last: 14" Here, even though the "last" is 14, "i" does not stop at 14, but goes on till first (= 10)+14 = 24. -- Any insights on why this is happening?
Operator precedence. first + 2:last is the same as first + (2:last) When first is 10 and last is 14, this is a sequence from 12 to 24. Duncan Murdoch ______________________________________________ R-help@r-project.org mailing list 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.
