Python – Remove Element by Value in Deque

In this tutorial, we will look at how to remove an element by value from a deque in Python with the help of some examples.

deque in Python

The collections module in Python comes with a deque class that you can use to implement a stack or queue data structure in Python. Deques support thread-safe, memory efficient appends and pops from either side of the deque with approximately the same O(1) performance in either direction.

In simple terms, you can think of a deque in Python as a list-like data structure but with efficient insertion and removal of items from either end (left and right). This makes them very useful when implementing a stack or queue functionality in Python.

How to remove an element by value from a deque in Python?

The deque class comes with a number of built-in functions to help perform common operations (like adding and removing elements).

To remove an element by value from a deque in Python, use the deque remove() function. Pass the element you want to remove as an argument. The following is the syntax –

# remove element "e" from deque "queue"
queue.remove(e)

It removes the first occurrence of the element e in the deque.

Examples

Let’s now look at some examples of using the above syntax –

Example 1 – Remove an element by value from a deque

First, let’s create a deque with some elements.

from collections import deque

# create a deque
queue = deque([1, 2, 3])
# print the deque
print(queue)

Output:

deque([1, 2, 3])

Here, we imported the deque class from the collections module and created a deque object, queue with three elements – 1, 2, and 3.

Now, let’s now remove the element 2 from the deque created above.

# remove element 2 from deque
queue.remove(2)
# print the deque
print(queue)

Output:

deque([1, 3])

Here, we used the deque remove() function to remove all the element 2 from the deque queue.

Let’s look at an example.

# create a deque
queue = deque([1, 2, 3, 2, 4])
# remove element 2 from deque
queue.remove(2)
# print the deque
print(queue)

Output:

deque([1, 3, 2, 4])

Here, the deque queue contains the element 2 at two different indices. When we use the deque remove() function and pass 2, the first occurrence of the element is removed from the deque.

To remove all the occurrences of an element from a deque, use the remove() inside a while loop like below.

# create a deque
queue = deque([1, 2, 3, 2, 4])
# remove all occurrences of a value from deque
val = 2
while val in queue:
    queue.remove(val)
# print the deque
print(queue)

Output:

deque([1, 3, 4])

All the occurrences of the element 2 is removed.

Example 2 – Remove an element not present in the deque

Let’s now try to remove an element that is not present in a deque.

# create a deque
queue = deque([1, 2, 3])
# remove element 4 from deque
queue.remove(4)
# print the deque
print(queue)

Output:

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
Input In [7], in <module>
      2 queue = deque([1, 2, 3])
      3 # remove element 4 from deque
----> 4 queue.remove(4)
      5 # print the deque
      6 print(queue)

ValueError: deque.remove(x): x not in deque

Here, we created a deque with elements 1, 2, and 3 and then used the remove() function to remove the element 4 (which is not present in the deque). Since the element is not in the deque, we get a ValueError.

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