Map

• map(function, iterable)
• Applies a function to each object in an iterable
• Returns a map object of results ( an iterator), which can be passed to list() or set()
• Printing out a map function directly gives an error. It needs to be converted to a list, tuple, etc. for readability.

# Program to double all numbers in a list
list_var = [1,2,3,4,5]
result = map(labmda x : x+x, list_var)
print(list(result))
# output: [2,3,6,8,10]

Filter

• filter(function, iterable)
• Returns the iterable values that match the condition specified in the function.
• The function passed to filter should return a Boolean

names = ["John", "Ana", "Jack",  "Kevin"]
print(list(filter(lambda x: x.startswith("J"), names)))
# ["John", "Jack"]

Reduce

• Import it first → from functools import reduce

• reduce(function, iterable)

• Applies a particular function passed in its argument to all of the elements in the iterable: below are the steps:

  1. First two elements of sequence are picked and the result is obtained by applying the function.
  2. Apply the same function to the previously attained result and the number just succeeding the second element and the result is again stored.
  3. Process continues till no more elements are left in the container.
  4. Final returned result is returned and printed on console.

  # Sum of elements
  list_var = [1, 3, 5, 6, 2, ]
  print(reduce(lambda x,y:x+y,list_var))