How Can I Efficiently Identify Consecutive Number Groups in a Python List?

Identifying Consecutive Number Groups in a List

When faced with the task of identifying groups of consecutive numbers within a list, there are multiple approaches to consider.

Inbuilt Python Functionality

Python provides a powerful tool for this task: the groupby() function. Utilizing this function, we can categorize elements based on the difference between their index and value. For instance, in the list [2, 3, 4, 5, 12, 13, 14, 15, 16, 17], the groupby() function would output the following groups:

[(2, [2, 3, 4, 5]), (12, [12, 13, 14, 15, 16, 17])]

Here, each group consists of elements whose index differs from their value by the same amount, indicating consecutive numbers.

Custom Function

An alternative approach involves creating a custom function. One implementation is given below:

ranges = []
for key, group in groupby(enumerate(data), lambda (index, item): index - item):
    group = map(itemgetter(1), group)
    if len(group) > 1:
        ranges.append(xrange(group[0], group[-1]))
    else:
        ranges.append(group[0])

This function generates a list of tuples, where each tuple represents a consecutive number group. For the input [2, 3, 4, 5, 12, 13, 14, 15, 16, 17], the output would be:

[(2, 5), (12, 17), 20]

Note that individual numbers are returned as individual elements rather than ranges.

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