Just asking anybody figured out, how to find high low for a period of time. Say in a period of 6months, starting from a initial point, next point could be a high or low, if high, program needs to find next lowest point and afterward, it needs to find highest amd continues to do so in zigzag. For low it's vice versa.
I think what you are asking is given a time series (x_0, x_1... x_n), what is the 6 month high (or low) on day i? In other words you want the max (or min) of the sub series (x_{i-180},x_{i-179}... x_i).
x_0 is obviously the 6 month high at day 0 (since there is no previous data). If x_1 > x_0 then x_1 is the new 6 month high so we can discard x_0 on day 1. If x_1 < x_0 then x_0 is still the 6 month high on day 1, but we cannot discard x_1 because it might become the 6 month high when x_0 expires on day 181. So we need to maintain some sort of data structure of potential 6 month highs such that we can lookup the current high and remove these highs as they expire or get replaced. The easiest way to do this is with a list of pairs [(x_i1, i1), (x_i2, i2)...] sorted by increasing x_i. Because it is sorted, the current high is always found on the element closest to the end of the list. Furthermore when a new element (x_k, k) is added, it replaces all the elements which come before it (thus they can be removed). As a corollary, because the newest element is always added to the back (after removing what's in front of it), the list is also sorted by order of expiry (with the oldest (x_i,i) at the end). Start with an empty list and i = 0
Find the sorted insertion point in the list for (x_i,i).
Remove everything prior to the insertion point.
Insert (x_i, i) at the start of the list.
If the element at the end of the list (x_n, n) is expired (n < i+180) then remove it.
The 6 month high on day i is found in the element at the end of the list. Store this in a new series h_i.
Increment i by 1 and repeat.
This method trivially works for finding the 6 month low as well.
You can do it in a single pass fairly easily. Loop over the rows of data. Store the current high to low, as well as the largest high to low since inception. If the current exceeds the largest since inception, simply replace it. Should be about 30 lines of code.
