ল্যাম্বডা, ম্যাপ এবং ফিল্টার (Lambda, Map & Filter)

# Regular function
def double(x):
    return x * 2

# Same thing as a lambda
double_lambda = lambda x: x * 2

print(double(5))         # 10
print(double_lambda(5))  # 10

# Lambda with multiple parameters
add = lambda a, b: a + b
print(add(3, 7))         # 10

# Lambda with a conditional expression
category = lambda age: "adult" if age >= 18 else "minor"
print(category(25))      # adult
print(category(12))      # minor

# Most useful: inline with sorted()
students = [("Anika", 92), ("Rafi", 85), ("Sadia", 97)]
by_score = sorted(students, key=lambda s: s[1], reverse=True)
print(by_score)

10
10
10
adult
minor
[('Sadia', 97), ('Anika', 92), ('Rafi', 85)]

# Square every number
numbers = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x ** 2, numbers))
print("Squared:", squared)

# Convert strings to integers
str_numbers = ["10", "20", "30", "40"]
int_numbers = list(map(int, str_numbers))  # Built-in function as argument!
print("Integers:", int_numbers)

# Temperature conversion: Celsius → Fahrenheit
celsius = [0, 20, 37, 100]
fahrenheit = list(map(lambda c: round(c * 9/5 + 32, 1), celsius))
print("Fahrenheit:", fahrenheit)

# map with multiple iterables
names = ["anika", "rafi", "sadia"]
greetings = ["hi", "hello", "hey"]
result = list(map(lambda g, n: f"{g.title()}, {n.title()}!", greetings, names))
print(result)

Squared: [1, 4, 9, 16, 25]
Integers: [10, 20, 30, 40]
Fahrenheit: [32.0, 68.0, 98.6, 212.0]
['Hi, Anika!', 'Hello, Rafi!', 'Hey, Sadia!']

# Filter even numbers
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
evens = list(filter(lambda x: x % 2 == 0, numbers))
print("Evens:", evens)

# Filter non-empty strings
words = ["", "hello", "", "world", "  ", "python"]
non_empty = list(filter(lambda w: w.strip(), words))
print("Non-empty:", non_empty)

# Filter passing scores
scores = {"Anika": 92, "Rafi": 58, "Sadia": 74, "Tariq": 45, "Esha": 88}
passing = dict(filter(lambda item: item[1] >= 60, scores.items()))
print("Passing:", passing)

# reduce() — combine all items into one value
from functools import reduce

nums = [1, 2, 3, 4, 5]
product = reduce(lambda a, b: a * b, nums)
print(f"\nProduct of {nums}: {product}")  # 1*2*3*4*5 = 120

# reduce to find longest word
words = ["cat", "elephant", "dog", "hippopotamus", "ant"]
longest = reduce(lambda a, b: a if len(a) > len(b) else b, words)
print(f"Longest word: {longest}")

Evens: [2, 4, 6, 8, 10]
Non-empty: ['hello', 'world', 'python']
Passing: {'Anika': 92, 'Sadia': 74, 'Esha': 88}

Product of [1, 2, 3, 4, 5]: 120
Longest word: hippopotamus

# Sort strings by length
fruits = ["জাম", "kiwi", "strawberry", "fig", "আম"]
by_length = sorted(fruits, key=lambda f: len(f))
print("By length:", by_length)

# Sort dicts by a specific field
students = [
    {"name": "Anika", "gpa": 3.8},
    {"name": "Rafi", "gpa": 3.2},
    {"name": "Sadia", "gpa": 3.9},
    {"name": "Tariq", "gpa": 3.5},
]
honor_roll = sorted(students, key=lambda s: s["gpa"], reverse=True)
for s in honor_roll:
    print(f"  {s['name']}: {s['gpa']}")

# Sort by multiple criteria (GPA desc, then name asc)
students.append({"name": "Esha", "gpa": 3.8})
multi_sort = sorted(students, key=lambda s: (-s["gpa"], s["name"]))
print("\nMulti-sort:")
for s in multi_sort:
    print(f"  {s['name']}: {s['gpa']}")

By length: ['fig', 'kiwi', 'আম', 'জাম', 'strawberry']
  Sadia: 3.9
  Anika: 3.8
  Tariq: 3.5
  Rafi: 3.2

Multi-sort:
  Sadia: 3.9
  Anika: 3.8
  Esha: 3.8
  Tariq: 3.5
  Rafi: 3.2