Fastest way to find the number of elements within a certain interval using two lists

Question

I have two lists called intervals and TIME. For each t in intervals, I define an interval (t-dt/2 and t+dt/2) and I want to calculate how many elements in TIME fall into that interval. Basically what I do is calculate the time bins. The below code is doing that, but I have a problem.

counts = []
for t in intervals:
    # Define time interval bounds
    lower_bound = t - dt / 2
    upper_bound = t + dt / 2
    # Count number of elements in TIME that fall within interval
    count = np.sum(np.logical_and(TIME > lower_bound, TIME < upper_bound)) # Counts the true
    counts.append(count)

This generates boolean list and count on the number. However, I need a numerical value where I also need to divide the number by list3[n] where n is the corresponding value for true return.

For example, if TIME[n] > lower_bound, TIME[n] < upper_bound, I just don’t want to be counted as 1, but I also want to divide it by list3[n].

I’m not sure how can I implement it here or if there is a faster way to do it. Using brute force takes a lot of time since these lists are pretty big. This was the fastest I could find, but now I don’t know how to divide each corresponding true return by corresponding list3[n]. Thanks for any help!

Edit: To give an example, say that t in interval is 1 and dt is 0.1. I want to find which elements in TIME list stay in that interval [0.9, 1.1]. The above code does that and counts how many elements of TIME stay in that interval.

However, I also have another list, called list3 that needs to divide corresponding TIME values. For example, if TIME=[0.8, 0.9, 1.0, 1.1, 1.2] and list3=[0.1, 0.2, 0.3, 0.4, 0.5] then the following is needed,

sum=1/list3[1]+1/list3[2]+1/list3[3]. Note that I do not include TIME[0] and TIME[4] since it is not in the interval.

Asked By: Thunder Owl

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Answer 1

this can easily be done using np.where

reciprocal_list3 = 1/list3  # do this line outside of the loop
count = np.sum(
    np.where(np.logical_and(TIME > lower_bound, TIME < upper_bound),
             reciprocal_list3, 0)
)

simply put, whenever the logical value of the comparison is True, it will grab that same index from reciprocal_list3 to use in the sum.

Answered By: Ahmed AEK

Fastest way to find the number of elements within a certain interval using two lists

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