 # create a list of lists. modify elements in the list

• Last Update :
• Techknowledgy :

Let’s start from basic, quickest way to create and initialize a normal list with same values in python is,

```# Creating a list with same values
list_of_num =  * 10

print(list_of_num)```

`[5, 5, 5, 5, 5, 5, 5, 5, 5, 5]`

Let’s inserting an element in the 3rd sub list of main list i.e.

```# Insert 11 into the 3 rd sub list
list_of_num.append(11)```

Let’s insert the element in the 3rd sub list,

```# Insert 11 into the 3 rd sub list
list_of_lists.append(11)

print(list_of_lists)```

Using Python’s range() function, we can generate a sequence of numbers from 0 to n-1 and for each element in the sequence create & append a sub-list to the main list using List Comprehension i.e.

```# Create a list of 5 empty sub lists
list_of_lists = [
[]
for i in range(5)
]

print('List of lists:')
print(list_of_lists)```

Suggestion : 2

Problem: How to create a list of lists by modifying each element of an original list of lists?,Problem: Given a list of lists. How to flatten the list of lists by getting rid of the inner lists—and keeping their elements?,Problem: How to print a list of lists with a new line after each list so that the columns are aligned?,Problem: How to convert a list of lists into a list of tuples?

For example, to create a list of lists of integer values, use `[[1, 2], [3, 4]]`. Each list element of the outer list is a nested list itself.

```lst = [
[1, 2],
[3, 4]
]```

Find examples of all three methods in the following code snippet:

```lst = [
[1, 2],
[3, 4]
]

# Method 1: List Comprehension
flat_1 = [x
for l in lst
for x in l
]

# Method 2: Unpacking
flat_2 = [ * lst, * lst]

# Method 3: Extend Method
flat_3 = []
for l in lst:
flat_3.extend(l)

# # Check results:
print(flat_1)
#[1, 2, 3, 4]

print(flat_2)
#[1, 2, 3, 4]

print(flat_3)
#[1, 2, 3, 4]```

Solution: You can achieve this by using the beautiful (but, surprisingly, little-known) feature of dictionary comprehension in Python.

```persons = [
['Alice', 25, 'blonde'],
['Bob', 33, 'black'],
['Ann', 18, 'purple']
]

persons_dict = {
x: x[1: ]
for x in persons
}
print(persons_dict)
# {
'Alice': [25, 'blonde'],
# 'Bob': [33, 'black'],
# 'Ann': [18, 'purple']
}```

Here’s the alternative code:

```persons = [
['Alice', 25, 'blonde'],
['Bob', 33, 'black'],
['Ann', 18, 'purple']
]

persons_dict = {}
for x in persons:
persons_dict[x] = x[1: ]

print(persons_dict)
# {
'Alice': [25, 'blonde'],
# 'Bob': [33, 'black'],
# 'Ann': [18, 'purple']
}```

Example: Convert the following list of lists

```[
[1, 2, 3],
[4, 5, 6]
]```

Suggestion : 3

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Python provides an option of creating a list within a list. If put simply, it is a nested list but with one or more lists inside as an element.

Here is an example of a list of lists to make things more clear:

```[
[a, b],
[c, d],
[e, f]
]```

#### Input:

```# Create 2 independent lists
list_1 = [a, b, c]
list_2 = [d, e, f]

# Create an empty list
list = []

# Create List of lists
list.append(list_1)
list.append(list_2)
print(list)```

#### Output:

```[
[a, b, c],
[d, e, f]
]```

Suggestion : 4

Last Updated : 01 Aug, 2022

Output:

`["Geeks", "for", "Geeks"]`

```Blank List: []

List of numbers: [10, 20, 14]

List Items:
Geeks
Geeks```

```Blank List: []

List of numbers: [10, 20, 14]

List Items:
Geeks
Geeks```

```List with the use of Numbers: [1, 2, 4, 4, 3, 3, 3, 6, 5]

List with the use of Mixed Values: [1, 2, 'Geeks', 4, 'For', 6, 'Geeks']```

```Accessing a element from the list
Geeks
Geeks```

```Accessing a element from a Multi - Dimensional list
For
Geeks```