How to Identify Consecutive Number Groups in Python Lists?

Identifying Consecutive Number Groups

In Python, identifying consecutive number groups within a list can be achieved using the built-in itertools.groupby() function. Here's how it works:

itertools.groupby() Function

The groupby() function groups elements of an iterable based on a key function. In this case, we define a key function that calculates the difference between an element's index and its value. Consecutive numbers will have the same key, leading to their grouping.

Code Implementation:

Consider the sample list [2, 3, 4, 5, 12, 13, 14, 15, 16, 17, 20]. The code below utilizes groupby() to identify consecutive number groups:

from itertools import groupby
from operator import itemgetter

data = [2, 3, 4, 5, 12, 13, 14, 15, 16, 17, 20]
ranges = []

for k, g in groupby(enumerate(data), lambda (i, x): i - x):
    group = map(itemgetter(1), g)
    if len(group) > 1:
        ranges.append(tuple(group[0], group[-1]))
    else:
        ranges.append(group[0])

Understanding the Key Function:

The lambda function (lambda (i, x): i - x) calculates the difference between an element's index (i) and value (x). This difference allows us to group consecutive numbers together. For instance, for the number 2, the difference would be 0, and for the number 12, the difference would be 10.

Processing Grouped Elements:

For each key (difference), groupby() produces a generator object (g) containing the corresponding grouped elements. We convert this generator to a list using map() and itemgetter() to extract only the element values.

Filtering and Appending Results:

We check the length of the grouped elements to determine if it's greater than 1, indicating consecutive numbers. If so, we append a tuple of the first and last elements in the group to the ranges list. For individual numbers, we append the number itself.

Output:

The ranges list will contain the following groups of consecutive numbers:

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

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