Check out example codes for "cluster on lists of values that start with a certain value". It will help you in understanding the concepts better.

Code Example 1

def grouper(iterable):
    prev = None
    group = []
    for item in iterable:
        if not prev or item - prev <= 15:
            group.append(item)
        else:
            yield group
            group = [item]
        prev = item
    if group:
        yield group

numbers = [123, 124, 128, 160, 167, 213, 215, 230, 245, 255, 257, 400, 401, 402, 430]
dict(enumerate(grouper(numbers), 1))

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