answers.py

from functools import reduce

# count
reduce(lambda i, _: i + 1, [1, 2, 3, 4, 5, 6, 2, 3], 0)

# max
reduce(lambda a, b: a if a > b else b, [1, 2, 3, 4, 5, 6, 2, 3])

# min
reduce(lambda a, b: a if a < b else b, [1, 2, 3, 4, 5, 6, 2, 3])

# sum
reduce(lambda i, a: i + a, [1, 2, 3, 4, 5, 6, 2, 3])

# remove
filter(lambda i: i % 3 != 0, [1, 2, 3, 4, 5, 6, 2, 3])

# flatten
reduce(
    lambda output, kv: output + kv,
    {'a': [1, 2], 'b': [3, 4], 'c': [5, 6]}.values(),
    []
)


# group
def group(groups, i):
    if (len(groups[-1]) < 3):
        groups[-1].append(i)
    else:
        groups.append([i])
    return groups


reduce(group, [1, 2, 3, 4, 5, 6, 2, 3], [[]])


# frequency
def frequency(result, i):
    if i not in result:
        result[i] = 1
    else:
        result[i] += 1
    return result


reduce(frequency, [1, 2, 3, 4, 5, 6, 2, 3], {})


# split
def split(result, i):
    if i % 2 == 0:
        result[0].append(i)
    else:
        result[1].append(i)
    return result


reduce(split, [1, 2, 3, 4, 5, 6, 2, 3], [[], []])


# group_by
def group_by_age(groups, i):
    if i['age'] not in groups:
        groups[i['age']] = [i]
    else:
        groups[i['age']].append(i)
    return groups


reduce(group_by_age, [
    {'age': 1, 'name': 'Alice'},
    {'age': 2, 'name': 'Bob'},
    {'age': 2, 'name': 'Clark'}
], {})

recursive.py

def group_recursive(items, groups=[[]]):
    if len(items) == 0:
        return groups

    if len(groups[-1]) < 3:
        groups[-1].append(items[0])
    else:
        groups.append([items[0]])

    return group_recursive(items[1:], groups)


print(group_recursive([1, 2, 3, 4, 5, 6, 2, 3]))