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pythonfor-looplist-comparison
Daniel van den Corput
Daniel van den Corput

Reputation: 13

Python: How to check if value is in between multiple indices of two lists?

I am analysing a video frame by frame with cv2, in which I want to save the frame as 1 if the frame number is in between certain timestamps and as 0 if not. I've got two lists, one with the start times and one with the end times:

start_times = [0, 10, 15]
end_times = [2, 12, 17]

I want to save the frame as 1 for frame numbers 0,1,2 & 10,11,12 & 15,16,17 and as 0 for the others.

My code saves the correct frames as 1, but it saves unwanted frames as 0 because I'm using a for loop. See the simplified example below:

start_times = [0,10,15]
end_times = [2,12,17]

currentframe = 0

while True: 
    try:
        for index,time in enumerate(start_times):
            if start_times[index] <= currentframe <= end_times[index]:
                print('save images as 1')
            else:
                print('save images as 0')
        currentframe += 1

        if currentframe == 20:
            break

    except IndexError:
        break

Which outputs for the first frame:

save images as 1
save images as 0
save images as 0

How can I change my code so the first frame is saved only as 1?

Upvotes: 0

Views: 607

Answers (3)

VIVID
VIVID

Reputation: 585

I'm not sure if I clearly understood you, but try this and tell me if it is what you want:

start_times = [0,10,15]
end_times = [2,12,17]

times = sorted(start_times + end_times)
print(times)

i = 0
while i + 1 < len(times):
  k = times[i]
  while k <= times[i + 1]:
    if i % 2 == 0:
      print('save [frame {}] as 1'.format(k))
    else:
      print('save [frame {}] as 0'.format(k))    
    k += 1
  i += 1

Upvotes: 1

Daniel van den Corput
Daniel van den Corput

Reputation: 13

A friend of mine has given me the solution by using ranges:

current_frame = 0
start_times = [0, 10, 15]
end_times = [2, 12, 17]
ranges = [range(start, stop) for start, stop in zip(start_times, end_times)]

while True:
    if any([current_frame in my_range for my_range in ranges]):
        print('save image as 1')
    else:
        print('save image as 0')
...

Upvotes: 0

go2nirvana
go2nirvana

Reputation: 1638

I think this is what you are looking for?

while curr_frame < 20:
    is_in = any(filter(lambda start_end: start_end[0] <= curr_frame <= start_end[1],
                       zip(start_times, end_times))))
    print(f'Save image as {int(is_in)}')
    curr_frame += is_in

Upvotes: 0

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