nHow to print out the first character of each list in Python?

A Python list is a built-in, mutable datatype that stores multiple items or elements, separated by commas, within square brackets [ ]. The index of a list in Python starts from 0 up to length-1. We can retrieve/access elements at a particular index as follows ?

list_name[index] 

The given task is to write a Python program that prints the first character of each element in a list. But, before that, let's see some example scenarios:

Scenario 1

For example, if our list contains string values, the output should be the first character of each string.

Input: names = ['aaa','bbb','ccc']
Output: new_list = [a, b, c]
Explanation:
Look at the input list, it has 3 strings. 
The first string starts with character 'a' 
The second one with 'b' 
The third one with 'c'. Hence, the output is [a, b, c].  

Scenario 2

Similarly, if our list contains (sub) lists, the output should be the first element of each sublist.

Input: numbers = [[12, 123, 1234], [9, 98, 987], [56, 456, 3475]]
Output: new_list = [12, 9, 56]
Explanation:
The input list has 3 sublists. 
The first element of 1st sublist is '12'
The first element of 2nd sublist is '9' 
The first element of the 3rd sublist is '56'. Therefore, the result would be [12, 9, 56]

Using a for Loop

In Python, using the for loop, we can iterate through each element in any iterable object. To print or retrieve the first characters of each element in a list, we need to iterate through its elements and access the character at index 0.

Example 1: First Element from Sublists

In the following Python program, we are defining a list of lists, and then using a for loop, we are printing the first element of each sublist ?

numbers = [[1,1,1],[2,2,2],[3,3,3]]
print("First element of each list:")
first_elements = []

for sublist in numbers:
    first_elements.append(sublist[0])
    
print(first_elements)

First element of each list:
[1, 2, 3]

Example 2: First Character from Strings

In this example, let us define a list with string values, and obtain the first character of each string using the for loop ?

names = ['apple','banana','cherry']
print("First character of each string:")
first_chars = []

for string in names:
    first_chars.append(string[0])
    
print(first_chars)

First character of each string:
['a', 'b', 'c']

Using List Comprehension

The list comprehension in Python helps us to create a list by performing an operation on each element of an iterable. To retrieve the first character of each element, we use element[0] as an operation on the desired list.

Example

In the following example, we are extracting the first element of each sublist using list comprehension ?

numbers = [[1,2,3],[4,5,6],[7,8,9]]
print("First element of each list:")

first_elements = [sublist[0] for sublist in numbers]
print(first_elements)

First element of each list:
[1, 4, 7]

Using map() Function

The Python map() function accepts a function and an iterable as parameters, applies the specified function to each item in the given iterable. To find the first character from each element in a list, we pass a lambda function to map().

Example

In the following example, we are extracting the first element of each sublist using the map() function ?

numbers = [[1,1,1],[2,2,2],[3,3,3]] 
print("First element of each list:")

first_elements = list(map(lambda s: s[0], numbers))
print(first_elements) 

First element of each list:
[1, 2, 3]

Comparison

Conclusion

Python provides multiple ways to extract the first character or element from each item in a list. List comprehension offers the most Pythonic and efficient approach, while for loops provide better readability for complex operations.