How to Sort Strings Containing Numbers Naturally in Python?

Sorting Strings with Embedded Numbers

When dealing with strings that contain numbers, sorting them alphabetically may not yield the desired results. To correctly sort such strings, you need to consider both the textual and numerical components.

Human Sorting (Natural Sorting)

Natural sorting, also known as human sorting, is a technique used to sort items in a way that is consistent with how humans perceive them. This approach involves extracting the numbers from the strings and then sorting them based on their numerical values.

In Python, you can implement natural sorting using the following custom sorting key:

def natural_keys(text):
    return [int(c) if c.isdigit() else c for c in re.split(r'(\d+)', text)]

This function splits the string into characters and numbers and then converts the numerical characters to integers. The sorted list is obtained by calling the sort() function with this custom key:

alist = ["something1", "something12", "something17", "something2", "something25", "something29"]
alist.sort(key=natural_keys)
print(alist)

The output would be:

['something1', 'something2', 'something12', 'something17', 'something25', 'something29']

Sorting Strings with Floats

If your strings contain floating-point numbers, you can modify the natural sorting key to extract and convert to floats using the following regex:

def natural_keys(text):
    return [float(c) if c.isdigit() else c for c in re.split(r'[+-]?([0-9]+(?:[.][0-9]*)?|[.][0-9]+)', text)]

This modified key allows you to sort strings with floating-point numbers as well:

alist = ["something1", "something2", "something1.0", "something1.25", "something1.105"]
alist.sort(key=natural_keys)
print(alist)

The output would be:

['something1', 'something1.0', 'something1.105', 'something1.25', 'something2']

By utilizing human sorting techniques, you can efficiently sort strings with embedded numbers in a way that aligns with human intuition.

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