Splitting Lists into Groups in Python

While working with lists in Python, there can be situations that you need to split a list into 2 lists on the basis of some conditions. This is when the idea of bifurcation becomes helpful. We will see in this post, how we can split a list provided you with another filter list via a simple yet effect solution Python.

What Does It Mean to Bifurcate a List?

If you do not know what bifucation, spliting a list – here you go. The filter function matches the original list element-by-element against the value in the filter list. If the filter list has a value which evaluates to True, such as True itself, it places an element into the first group; otherwise not.

The Code

Here’s a Python function that bifurcates a list based on a filter list:

def bifurcate(lst, filter):
  return [
    [x for x, flag in zip(lst, filter) if flag],
    [x for x, flag in zip(lst, filter) if not flag]
  ]

Let’s break down the code step by step.

Understanding the Code

1. Function Definition:
   • The function bifurcate takes two parameters:
     • lst: The list of elements to be bifurcated.
     • filter: The list of boolean values (or truthy/falsy values) used to determine the group assignment.
2. Using zip():
   • The zip(lst, filter) function pairs each element in lst with the corresponding element in filter. This allows us to process the list and the filter simultaneously.
3. List Comprehensions:
   • Two list comprehensions are used to create the two groups:
     • The first list comprehension [x for x, flag in zip(lst, filter) if flag] collects elements from lst where the corresponding value in filter is truthy.
     • The second list comprehension [x for x, flag in zip(lst, filter) if not flag] collects elements from lst where the corresponding value in filter is falsy.
4. Returning the Result:
   • The function returns a list containing the two groups.

Example Usage

To illustrate the function, let’s consider an example where we have a list of strings and a filter list:

result = bifurcate(['beep', 'boop', 'foo', 'bar'], [True, True, False, True])
print(result)

The output will be:

[['beep', 'boop', 'bar'], ['foo']]

In this example:

• 'beep', 'boop', and 'bar' are added to the first group because their corresponding filter values are True.
• 'foo' is added to the second group because its corresponding filter value is False.

Use Case: Organizing a To-Do List

You could think its kind of a list with diferente tasks that are highlighted as important, separate from all the others… Using the bifurcate Function

tasks = ['Buy groceries', 'Call the bank', 'Clean the house', 'Pay bills']
importance = [True, False, False, True]

important_tasks, regular_tasks = bifurcate(tasks, importance)

print("Important tasks:", important_tasks)
print("Regular tasks:", regular_tasks)

Output:

Important tasks: ['Buy groceries', 'Pay bills']
Regular tasks: ['Call the bank', 'Clean the house']

In this case, the bifurcate function allows tasks to be tidily separated into one side or other and avoids high-priority tasks from being lost at all because you know where they are (the priority array) which also makes sorting work loads so much easier.

Wrapping It Up

This is a very straightforward way of dividing the list into two parts based on presence in filter list using bifurcate function. This function is a great Python programming tool if you are using it to organize tasks, classify data or manipulate elements. This is an easily understandable solution based on list comprehensions and the zip() function, which can be translated to use in many other cases just switching conditions in filter.