Examples for map and filter

lists2.py

#
#
# fold


# map
# create a duplicate of the given list
def dup(lst):
    result = [] 
    for el in lst:
        result = result + [el]
    return result


print(dup([1, 2, 3]))
print(dup(["A", "B", "C"]))

# double each element of the list
def doubleEach(lst):
    result = [] 
    for el in lst:
        result = result + [el * 2]
    return result


print(doubleEach([1, 2, 3]))
print(doubleEach(["A", "B", "C"]))

# given a string, converts it to uppercase

def to_upper(ch):
    return chr(ord(ch) - 32)

print(to_upper("a"))
print(to_upper("b"))
print(to_upper("c"))
print(to_upper("d"))


def uppercase(lst):
    result = ""
    for el in lst:
        result = result + to_upper(el)
    return result


print(uppercase("hello"))
print(uppercase("world"))

# given a list of names in lowercase, 
# produce a list of names with the 
# first character capitalized

def upper_first_ch(name):
    return to_upper(name[0]) + name[1:]

print(upper_first_ch("jheno")) # Jheno

def cap_names(lst):
    result = [] 
    for el in lst:
        result = result + [upper_first_ch(el)]
    return result

print(cap_names(["jheno", "joshua", "janice"]))

def initials(lst):
    result = [] 
    for el in lst:
        result = result + [el[0]]
    return result

def initials2(lst):
    result = "" 
    for el in lst:
        result = result + el[0]
    return result

print(initials2([ "Jedaiah", "Joel", "Lumagbas" ])) # "JJL"


# create a list of powers of two,
# given a list of exponents
def powers(lst):
    result = [] 
    for el in lst:
        result = result + [2 ** el]
    return result

print(powers([1, 2, 3])) # [2, 4, 8]

# filter


def dup_filter(lst):
    result = [] 
    for el in lst:
        if (True):
            result = result + [el]
    return result

print(dup_filter([1, 2, 3]))
print(dup_filter(["A", "B", "C"]))


# filter all of the negative numbers in a list

def negs(lst):
    result = []
    for el in lst:
        if (el < 0):
            result = result + [el]
    return result

print(negs([-1, 3, -6, 0, 1]))

# given a string, return the string without vowels

def is_vowel(ch):
    return ch == "a" or ch == "e" or ch == "i" or ch == "o" or ch == "u"

def no_vowels(lst):
    result = ""
    for el in lst:
        if (not is_vowel(el)):
            result = result + el
    return result

print(no_vowels("tumbler"))


# filters out all names that begin with "J"

def starts_with_j(name):
    return name[0] == "J"

def no_j(lst):
    result = []
    for el in lst:
        if (not starts_with_j(el)):
            result = result + [el]
    return result

print(no_j(["Nisha", "Monique", "Janice", "Joshua", "Dennis", "Jheno"]))

# ["Nisha", "Monique", "Dennis"]


# produces a list of powers of two
# given a list of exponents
# ignoring negative exponents


def powers_positive(lst):
    result = []
    for el in lst:
        if (el >= 0):
            result = result + [2 ** el]
    return result


print(powers_positive([-1, 3, -6, 0, 1]))