40.Example programs using Dictionaries

Program to count the number of occurrence(frequency) of each letters in a given string( histogram) ( university question)

S=input("Enter the string…..")
d=dict()
for c in S:
    d[c]=d.get(c,0)+1
print("letter count")
print(d)

Program to display the frequency of each word in a given string.(university qstn)

S=input("Enter the string…..")

S=S.split(" ") #splitting it into words

d=dict()

for w in S:

    d[w]=d.get(w,0)+1

print("word count")

print(d)

Write a Python program to create a dictionary of roll numbers and names of five students. Display the names in the dictionary in alphabetical order.(university question)

d={}

for i in range(5):

    rn=int(input("Enter roll number.."))

    name=input("Enter name …")

    d[rn]=name

l=list(d.items())

l.sort(key=lambda v:v[1])

print("name and roll number in sorted order of name")

for i in l:

    print(i[1],":",i[0]) 

Program to read name and phn numbers of ‘n’ customers and print the list in sorted order of names

n=int(input("Enter number of customers.."))

d={}

for i in range(n):

    nm=input("Enter name..")

    phn=int(input("Enter phn number…"))

    d[nm]=phn

l=list(d.items()) # creating a list

l.sort() # sorting the list in the order of name.. 

             #l.sort(key=lambda v:v[1]) will sort in the order of phone number

print("name and phn number in sorted order")

for i in l:

    print(i[0],":",i[1])

In the above program after printing the sorted list, read a name and delete that customer from the dictionary if present.

n=int(input("Enter number of customers.."))

d={}

for i in range(n):

    nm=input("Enter name..")

    phn=int(input("Enter phn number…"))

    d[nm]=phn

l=list(d.items()) # creating a list

l.sort() # sorting the list in the order of name.. 

             #l.sort(key=lambda v:v[1]) will sort in the order of phone number

print("name and phn number in sorted order")

for i in l:

    print(i[0],":",i[1])

k=input("Enter a name to search..")

if k not in d:

    print("Not found the name")

else: 

    print("Details..",k,":",d[k])

    del(d[k]) # deleting the entry

print("Dictionary after deletion")

print(d)

The following program uses a dictionary to convert hexadecimal number into binary.

hextobin={'0':'0000','1':'0001','2':'0010','3':'0011','4':'0100','5':'0101','6':'0110','7':'0111','8':'1000','9':'1001','A':'1010','B':'1011','C':'1100','D':'1101','E':'1110','F':'1111'}

n=input('Enter the hexadecimal number….')

bn=''

n=n.upper()

for d in n:

    h=hextobin.get(d)

    if h==None:

       print('Invalid Number')

       break

    bn=bn+hextobin[d]

else:

    print('Binary equivalent is..',bn)

Finding the mode of list of numbers

n=int(input("Enter..how many numebrs.."))

print("Enter {} numbers".format(n))

numbers=[]

for i in range(n):

    x=int(input())

    numbers.append(x)

ncount={}

for x in numbers:

    ncount[x]=ncount.get(x,0)+1

maxcount=max(ncount.values())

print('Mode..')

for k in ncount:

    if ncount[k]==maxcount:

        print(k)

A matrix which contains large number of zeros is called sparse matrix. A better way to represent sparse matrix is my storing only the non zero element and its index using a dictionary.

m=int(input("Enter the number of rows....."))

n=int(input("Enter the number of columns....."))

print("Enter the elements of the sparse matrix ...")

A=[[0 for c in range(n)]for r in range(m)]

for r in range(m):

    for c in range(n):

        A[r][c]=int(input())

D={}

for r in range(m):

    for c in range(n):

        if A[r][c]!=0: #storing the non zero elements in the dictionary

            D[r,c]=A[r][c]

           

print("The Sparse Matrix is.....")    

for i in A:

    print (i)

  

print("The Dictionary Representation is....." )    

print(D)

Write a Python code to create a function called list_of_frequency that takes a string and prints the letters in non-increasing order of the frequency of their occurrences. Use dictionaries.

def list_of_frequency(s):

    d=dict()

    for c in s:

        d[c]=d.get(c,0)+1

    print("letter count in the decresing order")

    l=list(d.items())

    l.sort(key=lambda x:x[1],reverse=True)

    print(l)

s=input("Enter the string…..")

list_of_frequency(s)

Write a Python program to combine two dictionary adding values for common keys. d1 = {'a':10, 'b': 20, 'c':30} d2 = {'a': 30, 'b': 20, 'd':40} Sample output: {'a': 40, 'b': 40, 'd': 40, 'c': 30}

( university question)

d1 = {'a': 10, 'b': 20, 'c': 30}

d2 = {'a': 30, 'b': 20, 'd': 40}

#updating d1 with modified values

for key in d1:

    d1[key]=d2.get(key,0)+d1[key]

for key in d2:

    if key not in d1:

        d1[key]=d2[key]

print(d1)

output

{'a': 40, 'b': 40, 'c': 30, 'd': 40}

Write a Python script to print a dictionary where the keys are numbers between 1 and 15 (both included) and the values are square of keys.( university question)

d=dict()
for x in range(1,16):
    d[x]=x**2
print(d)