Part 1 Map and Filter
In this exercise, try to come up with the answer without using IDLE/Python first. If there is an error, specify the cause and type of the error. Then type the expressions into IDLE to verify your answers. The objective is for you to understand why and how they work.
L = [9,2,1,3,4,5,6]
Expressions Output
map(lambda x: x > 2, L)
list(filter(lambda x:x>2,L))
tuple(map(lambda x: 'o' if x%2 else 'e',L))
list(filter(lambda x: 'o' if x%2 else 'e',L))
list(map(str,list(filter(lambda x:x%2,L))))
str(list(filter(lambda x:x>30,map(lambda x:x*x,L))))
Part 2 Scale/Square Tuples
>>> map(lambda x:x*x, L)
[81, 4, 1, 9, 16, 25, 36]
>>> map(lambda x:x*2, L)
[18, 4, 2, 6, 8, 10, 12]
Part 3 Sum Digits Square
We solved the “Sum Digits” problem of writing function sum(n) which returns the sum of all the digits in n before. Write an alternative implementation sds(n) using our version of map() and built-in function sum().
How about “Sum Digit Square”? Write a function sdss(n) which returns the sum of the square of every digit in n.
Part 4 Taylor Series
The Taylor series is an infinite sum of many terms, e.g.
How do we use our version of map() and sum() to compute the above without using loops or recursion?
Part 5 Reduce
def reduce(f, seq): if not seq:
return seq
first = seq[0] for i in seq[1:]:
first = f(first,i)
return first
Predict the output of the following function call:
reduce(lambda x,y:x+y,[1,2,3])
