How can I modulo when my numbers start from 1, not zero?

user_377031 0
Viewed 27753

I guess the solution for this is quite simple, but I've been thinking about it for a while and couldn't come up with an elegant solution.

I have a range of numbers, e.g. 1..10 = (1,2,3,4,5,6,7,8,9,10), which is circular, meaning the number after the last one is again the first one (next(10)=1).

For a given number i>0 in the range, I would like to calculate the next m-th, and previous m-th number. e.g. next(5,1)=6 next(10,1)=1 next(10,2)=2 prev(5,2)=3 prev(1,1)=10 prev(1,2)=9.

For next I can just take (i+m)%n where n is the length of the range (n=10 in the example). But for prev I couldn't find an elegant solution.

modulo
7 Answers

I have this solution in R:

pred <- function(n) n - 1L # cf. Pascal's pred
succ <- function(n) n + 1L # cf. Pascal's succ
`%mod1%` <- function(m, n) succ(pred(m) %% n) # modulo from 1
cat(-11:24 %mod1% 12) # test
# 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12
user_83412740

Say you want to map from 1 to n not 0 to n-1 eg n=5, range 1 to x, results 0 to 4,0mod5=0 1mod5=1, 2mod5=2... xmod5 results 0 whenever x=5*k. Use ((x-1)mod5)+1, x must be >0. This will always map (count) in 1 to 5 range, instead 0 to 4.

user_155090960
Related