Let’s learn some new Python concepts!. Map, Filter, lambda and Reduce are paradigms of functional programming. They allow the programmer (you) to write simpler, shorter code, without neccessarily needing to bother about intricacies like loops and branching.
Lambda is a single expression anonymous function often used as an inline function. In simple words, it is a function that has only one line in its body. It proves very handy in functional and GUI programming.
sum = lambda a, b, c: a + b + c print(sum(1, 2, 3)) # prints 6
map() function executes a specified function for each item in iterables(as many as they are). The item is sent to the function as a parameter.
Let’s say you are given a list of names, and you have to print a list that contains the length of each name.
print (list(map(len, ['Tina', 'Raj', 'Tom']))) # prints [4, 3, 3]
map() passes each element in the iterable through a function and returns the result of all elements having passed through the function,
filter(), first of all, requires the function to return boolean values (true or false) and then passes each element in the iterable through the function, “filtering” away those that are false.
Let’s see an example.
The following is a list
(iterable) of the scores of 10 students in an exam. Let’s filter out those who passed with scores more than 75…using
# Python 3 scores = [66, 90, 68, 59, 76, 60, 88, 74, 81, 65] def is_A_student(score): return score > 75 over_75 = list(filter(is_A_student, scores)) print(over_75)
reduce applies a function of two arguments cumulatively to the elements of an iterable, optionally starting with an initial argument.
Reduce is not in the
__builtins__ module, so it needs to be imported as it resides in the
reduce(func, iterable[, initial])
Say you have a list, say [1,2,3] and you have to find its sum.
from functools import reduce print(reduce(lambda x, y : x + y,[1,2,3])) # prints 6
You can also define an initial value. If it is specified, the function will assume initial value as the value given, and then reduce. It is equivalent to adding the initial value at the beginning of the list.
from functools import reduce print(reduce(lambda x, y : x + y, [1,2,3], -3)) # prints 3 from fractions import gcd print(reduce(gcd, [2,4,8], 3)) # prints 1
Try the following excerise in the editor below.
In this exercise, you’ll use each of
map, filter, and reduce to fix broken code.