List-Questions.py

# Create nested list with 10 elements where 4th element is nested list with 4 elements. Access all elements with indexing.
list1=[0,0,7,['J','P',2,2],9,9,5,'l','s','t']
print(list1[0])
print(list1[1])
print(list1[2])
print(list1[3])
print(list1[3][0])
print(list1[3][1])
print(list1[3][2])
print(list1[3][3])
print(list1[4])
print(list1[5])
print(list1[6])
print(list1[7])
print(list1[8])
print(list1[9])

# Create two lists and concatenate them.
list1=['J','P',2,2]
list2=['_',0,0,7]
print(list1+list2)

# Traverse a list.
list1=['Red','Green','Blue','Yellow','Black']
## For loop
### Method 1
for i in list1:
    print(i)
### Method 2
for i in range(len(list1)):
    print(list1[i])
## While loop
i=0
while i<len(list1):
    print(list1[i])
    i+=1

# Print elements of list in separate lines along with element's both indexes.
list1=['q','w','e','r','t','y']
for a in range(len(list1)):
    print('At indexes',a,'and',(a-len(list1)),'element present:',list1[a])

# Take two lists with elements as numbers from 1 to 20. Find sum of elements between indexes 5 to 15 in first list. Find average of every fourth element in second list.
l1=l2=[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]
l1new=l1[6:15:2]
l2new=l2[::4]
s1=s2=count=0
print('New first list:',l1new)
for i in l1new:
    s1+=i
print('Sum of elements between indexes 5 to 15 in first list:',s1)
print('New second list:',l2new)
for j in l2new:
    s2+=j
    count+=1
s2=s2/count
print('Average of every fourth element in second list:',s2)

# Make copy of list with 10 elements then add 10 to first and last element of copied list.
l1=[1,2,3,4,5,6,7,8,9,10]
l2=l1.copy()
l2[0]+=10
l2[9]+=10
print(l1,l2)

# Take input of elements from users and give smallest number and it's index.
## Method 1
l=[1,2,3,4,5,6,7,8,9,10]
for i in range(0,len(l)):
    m=min(l)
print('The smallest element is',m,'and it\'s index number is',l.index(m))
## Method 2
l=eval(input('Enter elements: '))
print('List given:',l)
print('Smallest element is',min(l),'and it\'s index number is',l.index(min(l)))
## Method 3
l=list(input('Enter elements: '))
print(l)
print('Smallest element is',min(l),'and it\'s index number is',l.index(min(l)))
## Method 4
l=eval(input('Enter elements: '))
l.sort()
print('List elements in ascending order:',l)
print('Smallest element is:',l[0],'and it\'s index number is:',l.index(min(l)))

# Find largest/max number in a list using sort
l=eval(input('Enter elements: '))
print('List given:',l)
l.sort()
print('Largest element is:',l[-1])

# Find average/mean of list
l=eval(input('Enter elements: '))
print('List given:',l)
print('Average of list elements:',(sum(l)/len(l)))

# Asks user to input numbers in list to be appended to existing list. Whether user extends single number/list of numbers, append into list accordingly.
l=[1,2,3,4]
print('Existing list:',l)
n=eval(input('Enter values: '))
if type(n)==type([]):
    l.extend(n)
elif type(n)==type(1):
    l.append(n)
else:
    print('Enter list or integer.')
print('New list:',l)

# Replicate list twice and arrange elements in ascending and descending order
l=eval(input('Enter elements for list: '))
l2=l.copy()
l3=l.copy()
print('Copy 1:',l2)
print('Copy 2:',l3)
l.sort()
print('List elements in ascending order:',l)
l.sort()
l.reverse()
print('List elements in descending order:',l)

# Search for element in list
l=eval(input('Enter elements: '))
e=eval(input('Enter element to search: '))
for i in range(0,len(l)):
    if l[i]==e:
        print('Yes, element is present at index position',l.index(e))
        break
    else:
        print('No, element is not present')

# Count frequency of element in list
l=eval(input('Enter elements: '))
e=eval(input('Enter element to search: '))
count=0
for i in range(0,len(l)):
    if l[i]==e:
        count+=1
print('Frequency of element:',count)

# Check if maximum element is in first or second half
l=eval(input("Enter elements: "))
if l.index(max(l))<=(len(l)/2):
    print("Maximum element",max(l),"is in first half.")
else:
    print("Maximum element",max(l),"is in second half.")

# Display max element of both lists combined along with index in list
l1=eval(input('Enter elements for list 1: '))
l2=eval(input('Enter elements for list 2: '))
print('List 1 given:',l1,'and it\'s maximum element:',max(l1),'and it\'s index number:',l1.index(max(l1)))
print('List 2 given:',l2,'and it\'s maximum element:',max(l2),'and it\'s index number:',l2.index(max(l2)))
if max(l1)>max(l2):
    print('Maximum element of both lists is in list 1')
else:
    print('Maximum element of both lists is in list 2')

# Find sum of all odd and even numbers separately
l=eval(input('Enter elements: '))
es,os=0,0
for i in range(0,len(l)):
    if l[i]%2==0:
        es+=l[i]
    else:
        os+=l[i]
print('Sum of even elements:',es,'and sum of odd elements:',os)

# Find largest number in list
## Using sort
a=[]
n=int(input("Enter number of elements:"))
for i in range(1,n+1):
    b=int(input("Enter element:"))
    a.append(b)
a.sort()
print("Largest element is:",a[n-1])
## Using def
def maxnumlist(l):
    max=l[0]
    for i in l:
        if i > max:
            max = i
    return max
print(maxnumlist([1,2,-8,0]))

# Find mean of list
def avg(l):
    return sum(l)/len(l)
l=[15,9,55,41,35,20,62,49]
a=avg(l)
print("Average of list:",round(avg,2))

# Frequency of element in list
import collections
l=[101,101,101,101,201,201,201,201]
print("Original list: ",l)
ctr=collections.Counter(l)
print("Frequency of elements in list: ",ctr)