Summary  
This chapter explains how to perform element selection by combining comparison operators (`>`, `<`, `>=`, `<=`, `==`, `!=`) with logical operators (`&`, `|`) for boolean indexing.

General domain of usage  
Data analysis

Most conditions you will use are **comparisons**, so it's important to discuss them in more detail. Comparisons are based on the following comparison operators:
* `>` (greater than);
* `<` (less than);
* `>=` (greater than or equal to);
* `<=` (less than or equal to);
* `==` (equal to);
* `!=` (not equal to).

Moreover, you can **combine** multiple conditions and comparisons using the following logical operators:
* `&` (logical **and**);
* `|` (logical **or**).

If at least one of the conditions is `True`, then `|` returns `True`; otherwise, it returns `False`. If at least one of the conditions is `False`, then `&` returns `False`; otherwise, it returns `True`.

Each condition should be put in parentheses `()` when combining them.

Note

import numpy as np
# Creating an array of integers from 1 to 10 inclusive
array = np.arange(1, 11)
# Retrieving elements greater than or equal to 5 AND less than 9
print(array[(array >= 5) & (array < 9)])
# Retrieving elements less than or equal to 4 AND not equal to 2
print(array[(array != 2) & (array <= 4)])
# Retrieving elements less than 3 OR equal to 8
print(array[(array < 3) | (array == 8)])
# Retrieving elements between 2 inclusive AND 5 inclusive OR equal to 9
print(array[(array >= 2) & (array <= 5) | (array == 9)])

Let's now take a look at the following visualization to understand the code better (**red** squares represent the actual retrieved elements):

import unittest
import importlib.util
import numpy as np
import io
from contextlib import redirect_stdout


def _dynamic_test(test_case, condition, success_message, failure_message):
    """Codefinity-style result messages"""
    if condition:
        test_case._testMethodName = success_message
        test_case.assertTrue(True, success_message)
    else:
        test_case._testMethodName = failure_message
        test_case.fail(failure_message)


class TestUserCode(unittest.TestCase):
    @classmethod
    def setUpClass(cls):
        # Імпортуємо код користувача
        spec = importlib.util.spec_from_file_location("user_code", "user_code.py")
        cls.m = importlib.util.module_from_spec(spec)
        spec.loader.exec_module(cls.m)

        # Очікувані результати
        cls.product_ratings = np.array([4, 2, 5, 3, 7, 1])
        cls.expected_filtered = cls.product_ratings[
            (cls.product_ratings >= 3) & (cls.product_ratings != 5)
        ]

    def test_boolean_filter_correctness(self):
        """1. Перевірка правильності булевого фільтра"""
        # Перехоплюємо вивід користувача
        f = io.StringIO()
        with redirect_stdout(f):
            spec = importlib.util.spec_from_file_location("user_code", "user_code.py")
            module = importlib.util.module_from_spec(spec)
            spec.loader.exec_module(module)
        output = f.getvalue().strip()

        # Підготовка очікуваного текстового представлення
        expected_str = np.array2string(self.expected_filtered, separator=' ')
        # Перевіряємо, що всі елементи виведено правильно
        contains_values = all(str(x) in output for x in self.expected_filtered)

        _dynamic_test(
            self,
            contains_values and str(5) not in output and "2" not in output and "1" not in output,
            "Boolean indexing applied correctly",
            "Boolean indexing incorrect or wrong output",
        )


if __name__ == "__main__":
    unittest.main()


test_code.py

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