How Can I Extract the First Item from Each Sublist in a Python List of Lists?

Extracting First Item from Each Sublist in Python

In Python, when working with nested data structures like lists of lists, it may be necessary to extract specific elements from each sublist to create a new list. For instance, to extract the first item from each sublist in a list of lists, you can use the following methods:

1. List Comprehension:

This concise approach utilizes list comprehension to iterate through each sublist and append the first item to a new list.

lst = [['a', 'b', 'c'], [1, 2, 3], ['x', 'y', 'z']]
lst2 = [item[0] for item in lst]

2. Map and Lambda:

You can employ the map() function alongside a lambda function to achieve the same result. The lambda function retrieves the first item within each sublist.

lst = [['a', 'b', 'c'], [1, 2, 3], ['x', 'y', 'z']]
lst2 = list(map(lambda sublist: sublist[0], lst))

3. For Loop:

While slightly less efficient than the previous methods, a for loop can also accomplish the task.

lst = [['a', 'b', 'c'], [1, 2, 3], ['x', 'y', 'z']]
lst2 = []
for sublist in lst:
    lst2.append(sublist[0])

The appropriate choice depends on the specific requirements and performance considerations of your code. For simple and efficient scenarios, list comprehension or map() with lambda are commonly preferred.

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