5 Best Ways to Test if Elements of a List Are Within a Range Defined by Another List in Python

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💡 Problem Formulation: We often encounter situations in programming where we need to check whether the elements of one list fall within the range specified by the minimum and maximum values in another list. This is a common task, for example, when dealing with constraints in optimization problems or validating data. Suppose we have a list [3, 5, 9] and want to test each element against the range established by another list [2, 8]. The desired output would be a list of booleans such as [True, True, False] indicating which elements fall within the range.

Method 1: Using List Comprehension

An intuitive approach to check if elements from one list fall within a min-max range from another list is using list comprehension. List comprehension offers a concise way to create lists by iterating over an iterable and applying an expression to each item. Functionally, we iterate over each element and check its bounds against the min and max values provided.

Here’s an example:

elements = [3, 5, 9]
range_values = [2, 8]
result = [min(range_values) <= x <= max(range_values) for x in elements]
print(result)

Output:

[True, True, False]

This code snippet sets up two lists, elements and range_values, and uses list comprehension to evaluate each element of elements. The result is a new list, result, containing boolean values indicating whether each element is within the required range.

Method 2: Using the all() Function

The all() function checks if all elements of an iterable are true. We can apply it to verify if all elements of one list are within the range of the other by making an iterable of boolean conditions.

Here’s an example:

elements = [3, 5, 9]
min_val, max_val = [2, 8]
result = [all([min_val <= x, x <= max_val]) for x in elements]
print(result)

Output:

[True, True, False]

This piece of code uses unpacking to assign the minimum and maximum values, then employs all() within the list comprehension to ensure that each element satisfies both the minimum and maximum conditions, returning the corresponding boolean list.

Method 3: Using a For Loop and Conditional Statements

A straightforward method that provides clear and readable code is using a for loop combined with conditional statements to check if the list elements are within the provided range. Although not as concise as list comprehension, it may be easier for some to understand and follow.

Here’s an example:

elements = [3, 5, 9]
range_values = [2, 8]
result = []
for x in elements:
    result.append(range_values[0] <= x <= range_values[1])
print(result)

Output:

[True, True, False]

In this code snippet, a for loop iteratively tests each element in elements against the range set by range_values. The resulting boolean values are then appended to the result list.

Method 4: Using the filter() Function and Lambda

The filter() function is used to construct an iterator from elements of an iterable for which a function returns true. By combining filter() with a lambda function, we can selectively process items in our list that meet our range condition and then convert the result back into a list for output.

Here’s an example:

elements = [3, 5, 9]
range_values = [2, 8]
result = list(filter(lambda x: range_values[0] <= x <= range_values[1], elements))
is_in_range = [item in result for item in elements]
print(is_in_range)

Output:

[True, True, False]

Here, a lambda function is provided to the filter() function to create an iterator of items within the range. Then, we convert it to a list result. Finally, we use list comprehension to check which elements from the original elements list are in the result list, indicating if they’re within the range.

Bonus One-Liner Method 5: Using the in Operator with Range Creation

If the elements to be checked are integers and the range is also within integer bounds, Python’s range() function and the in operator can be combined for this purpose. This one-liner leverages the fact that range() can act as an iterable that produces a sequence of numbers.

Here’s an example:

elements = [3, 5, 9]
range_values = [2, 8]
result = [x in range(range_values[0], range_values[1]+1) for x in elements]
print(result)

Output:

[True, True, False]

This method uses list comprehension with the in operator to check if each integer element is in the range defined by range_values. Note that the upper bound in Python’s range is exclusive, hence +1.

Summary/Discussion

  • Method 1: List Comprehension. Fast and pythonic. Might be less readable to beginners.
  • Method 2: all() Function. Explicitly shows the logical “and” operation. Slightly less straightforward than list comprehension.
  • Method 3: For Loop and Conditional Statements. Very readable. More verbose and possibly slower than other methods.
  • Method 4: filter() Function and Lambda. Streams elements and is memory efficient. Can be obscure to those unfamiliar with functional programming concepts.
  • Method 5: in Operator with Range Creation. Works only with integers. Neat and clean but not as flexible as other methods.