Boolean Mask Indexing & Fancy Slicing

1Concept

Boolean indexing uses a boolean condition array to filter elements satisfying a predicate. Fancy indexing uses integer index arrays to extract arbitrary elements, creating a deep copy rather than a view.

2Architecture Diagram

Array:   [ 10, 25, 30, 45, 50 ]
Mask:    [  F,  T,  F,  T,  T ] (arr > 20)
Result:  [ 25, 45, 50 ]

3Code Example

data = [10, 25, 32, 18, 55, 40]
# Boolean filtering logic
threshold = 30
filtered = [x for x in data if x > threshold]
print(f"Original: {data}")
print(f"Filtered (data > {threshold}): {filtered}")

4Expected Output

Original: [10, 25, 32, 18, 55, 40]
Filtered (data > 30): [32, 55, 40]

5Key Takeaways

• ✓Boolean mask indexing creates a COPY, not a view.
• ✓Combine conditions using bitwise operators (`&` for AND, `|` for OR, `~` for NOT) with parentheses.
• ✓Fancy indexing (`arr[[0, 2, 4]]`) extracts arbitrary indices in specified order.