Indexing Tips: extend a time series to be cyclic

Hi everyone,

I'm trying to write some code to get stats on a time series and I'm looking for tips about handling negative and zero indices, i.e. I want an efficient way to tell Matlab that when an index is negative (say -n) to choose the element of the time series n+1 steps from the end. So far I'm using if statements but it's slowing down the code quite a bit.

Any advice?

-Tom

Answer 1

[Honglei Chen]

Not sure if it solves your question exactly but here is something that could be helpful. Say your data is 5 samples long

N = 5;
idx = -N:N
idx_new = mod(idx-1,N)+1

Answer 2

[Walter Roberson]

See http://www.mathworks.co.uk/matlabcentral/answers/44993-circular-indexing-of-an-array