Map & Filter¶
These are two functions which facilitate a functional approach to programming. We will discuss them one by one and understand their use cases.
Map applies a function to all the items in an input_list. Here is
Most of the times we want to pass all the list elements to a function one-by-one and then collect the output. For instance:
items = [1, 2, 3, 4, 5] squared =  for i in items: squared.append(i**2)
Map allows us to implement this in a much simpler and nicer way.
Here you go:
items = [1, 2, 3, 4, 5] squared = map(lambda x: x**2, items)
Most of the times we use lambdas with
map so I did the same. Instead
of a list of inputs we can even have a list of functions!
def multiply(x): return (x*x) def add(x): return (x+x) funcs = [multiply, add] for i in range(5): value = map(lambda x: x(i), funcs) print(value) # Output: # [0, 0] # [1, 2] # [4, 4] # [9, 6] # [16, 8]
As the name suggests, filter creats a list of elements for which a function returns true. Here is a short and consise example:
number_list = range(-5,5) less_than_zero = list(filter(lambda x: x<0, number_list)) print(less_than_zero) # Output: [-5, -4, -3, -2, -1]
The filter resembles a for loop but it is a builtin function and faster.
Note: If map & filter do not appear beautiful to you then you can