Python | Group strings at particular element in list

Python | Group strings at particular element in list

Grouping strings in a list based on a particular element or value can be useful for various data analysis or transformation tasks. This tutorial will walk you through the process of achieving this in Python.

Problem Statement:

Suppose we have a list of strings:

strings = ["apple_1", "banana_2", "cherry_1", "dragonfruit_3", "eggfruit_1", "fig_2"]

We aim to group the strings based on the digit that follows the underscore _:

Expected result:

{ '1': ['apple_1', 'cherry_1', 'eggfruit_1'], '2': ['banana_2', 'fig_2'], '3': ['dragonfruit_3'] }

Tutorial:

Method 1: Using a Regular Dictionary

  1. Initialize an empty dictionary.
  2. Iterate over the list of strings.
  3. For each string, split it at the underscore _ to isolate the digit.
  4. Use the digit as the key to group the string in the dictionary.
def group_by_element(strings): grouped = {} for s in strings: _, key = s.split('_') if key in grouped: grouped[key].append(s) else: grouped[key] = [s] return grouped strings = ["apple_1", "banana_2", "cherry_1", "dragonfruit_3", "eggfruit_1", "fig_2"] result = group_by_element(strings) print(result)

Method 2: Using defaultdict

This method uses defaultdict from the collections module to simplify and shorten the code:

from collections import defaultdict def group_by_element(strings): grouped = defaultdict(list) for s in strings: _, key = s.split('_') grouped[key].append(s) return dict(grouped) strings = ["apple_1", "banana_2", "cherry_1", "dragonfruit_3", "eggfruit_1", "fig_2"] result = group_by_element(strings) print(result)

Method 3: Using Dictionary Comprehension

For a more compact solution:

def group_by_element(strings): grouped = {} for s in strings: key = s.split('_')[1] grouped.setdefault(key, []).append(s) return grouped strings = ["apple_1", "banana_2", "cherry_1", "dragonfruit_3", "eggfruit_1", "fig_2"] result = group_by_element(strings) print(result)

Conclusion:

This tutorial introduced different ways to group strings in a list based on a particular element (in this case, the digit after an underscore). Whether using a regular dictionary, defaultdict, or dictionary comprehension, the concept remains the same: split the string to isolate the key and then aggregate the strings by that key.

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