Hackerrank - HackerRank Python Built-in Functions and Lambdas Questions and Answers

Question 1

A list of dictionaries needs to be sorted based on the 'age' of each person. Which of the following code snippets correctly performs this sort?

Accepted Answer

sorted(people, key=lambda person: person['age'])

Answer

The built-in `sorted()` function returns a new sorted list. It takes a `key` argument, which should be a function that takes one element and returns a value to sort by. A lambda function `lambda person: person['age']` is the perfect tool for this, as it takes a dictionary (`person`) and returns the value associated with the 'age' key for comparison.

Question 2

What is the primary characteristic that distinguishes a lambda function from a standard function defined with `def`?

Accepted Answer

A lambda function is restricted to a single expression and implicitly returns its result.

Answer

Lambda functions are syntactically restricted to a single expression. The value of this expression is what the function implicitly returns. In contrast, functions defined with `def` can contain multiple statements, including explicit `return` statements, loops, and assignments.

Question 3

Given a list of integers, `numbers = [10, 15, 21, 33, 42, 55]`, which line of code will produce a new list containing only the numbers divisible by 5?

Accepted Answer

list(filter(lambda x: x % 5 == 0, numbers))

Answer

The `filter()` built-in function is used to construct an iterator from elements of an iterable for which a function returns true. The lambda function `lambda x: x % 5 == 0` correctly tests each number for divisibility by 5, and `filter()` includes only those that pass the test. `map()` would apply the function to every element, returning a list of booleans, not the filtered numbers.

Question 4

What will be the output of the following Python code snippet?

```python
from functools import reduce

items =
result = reduce(lambda x, y: x * y, items)
print(result)
```

Accepted Answer

24

Answer

The `reduce` function from the `functools` module applies a function of two arguments cumulatively to the items of an iterable. In this case, `lambda x, y: x * y` multiplies the elements. The process is: 1*2=2, then 2*3=6, then 6*4=24. The final accumulated value is 24.

Question 5

A developer needs to create a new list where each number from an original list is tripled. Which of the following is the most idiomatic use of a built-in function with a lambda to achieve this?

Accepted Answer

list(map(lambda x: x * 3, original_list))

Answer

The `map()` function applies a given function to each item of an iterable and returns an iterator of the results. The lambda `lambda x: x * 3` is the function that triples a number. `map()` applies this to every element, creating the desired transformed list. `filter()` is for selection, not transformation.

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Hackerrank - HackerRank Python Built-in Functions and Lambdas Questions and Answers