In this post, we will see a different ways to reverse array in Python.
Let’s see the example first.
Example:
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Input : [10 20 30 40 50 60] Output : [60 50 40 30 20 10] |
As we know, Python language has not come up with an array data structure. So in python there are some ways to create an array like data structure. Some ways like: use list, use array module and use numpy module for array.
Using list
Now first, we will see different ways to reverse a list in Python.
You can use the list as array in python and perform various operations on the list to reverse it.
Using a concept of list slicing.
Here, we are using concept of Python list slicing to reverse a list. List slicing performs in-place reversal , so no extra space is required.
Below is the Python code given:
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# list arr = [10, 20, 30, 40, 50, 60] print("Original array is:", arr) # reverse the list using list slicing rev_arr = arr[: : -1] print("Reversed array is:", rev_arr) |
Output:
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Original array is: [10, 20, 30, 40, 50, 60] Reversed array is: [60, 50, 40, 30, 20, 10] |
Using a reverse() method of list.
Here, we are using reverse() method of list to reverse a list. reverse() method performs in-place reversal , so no extra space is required.
Below is the Python code given:
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# list arr = [10, 20, 30, 40, 50, 60] print("Original array is:", arr) # reverse the list using reverse() method arr.reverse() print("Reversed array is:", arr) |
Output:
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Original array is: [10, 20, 30, 40, 50, 60] Reversed array is: [60, 50, 40, 30, 20, 10] |
Using a reversed() built-in function.
Here, we are using reversed() function to reverse a list. This function returns reversed iterator object , so we convert it into list by using list() function.
Below is the Python code given:
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# list arr = [10, 20, 30, 40, 50, 60] print("Original array is:", arr) # reverse the list using reversed() function rev_arr = list(reversed(arr)) print("Reversed array is:", rev_arr) |
Output:
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Original array is: [10, 20, 30, 40, 50, 60] Reversed array is: [60, 50, 40, 30, 20, 10] |
Using array modile
Now, we will see different ways to reverse an array using array module in Python.
Using a reverse() method of array object.
Here, we are using reverse() method of list to reverse an array. reversed() method performs in-place reversal , so no extra space is required.
Below is the Python code given:
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# import array module import array # integer array arr = array.array('i',[10, 20, 30, 40, 50, 60]) print("Original array is:", arr) # reverse an array using reverse() method arr.reverse() print("Reversed array is:", arr) |
Output:
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Original array is: array('i', [10, 20, 30, 40, 50, 60]) Reversed array is: array('i', [60, 50, 40, 30, 20, 10]) |
Using a reversed() built-in function.
Here, we are using reversed() function to reverse an array. This function returns reversed iterator object ,so we convert it into array by using array.array() function.
Below is the Python code given:
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# import array module import array # integer array arr = array.array('i', [10, 20, 30, 40, 50, 60]) print("Original array is:", arr) # reverse an array using reversed() function rev_arr = array.array('i', reversed(arr)) print("Reversed array is:", rev_arr) |
Output:
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Original array is: array('i', [10, 20, 30, 40, 50, 60]) Reversed array is: array('i', [60, 50, 40, 30, 20, 10]) |
Using numpy array
Now, we will see a different ways to reverse a numpy array in Python.
Using a flip() method of numpy module.
Here, we are using flip() method of numpy to reverse a numpy array. `flip() method returns numpy array object.
Below is the Python code given:
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# import numpy module import numpy as np # numpy array arr = np.array([10, 20, 30, 40, 50, 60]) print("Original array is:", arr) # reverse an array using flip() method # 0 denotes horizonatl axis rev_arr = np.flip(arr, 0) print("Reversed array is:", rev_arr) |
Output:
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Original array is: [10 20 30 40 50 60] Reversed array is: [60 50 40 30 20 10] |
Using a concept of array slicing.
Here, we are using concept of slicing to reverse a numpy array. slicing performs in-place reversal , so no extra space is required.
Below is the Python code given:
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# import numpy module import numpy as np # numpy array arr = np.array([10, 20, 30, 40, 50, 60]) print("Original array is:", arr) # reverse an array using slicing rev_arr = arr[: : -1] print("Reversed array is:", rev_arr) |
Output:
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Original array is: [10 20 30 40 50 60] Reversed array is: [60 50 40 30 20 10] |
Using a flipud() method of numpy module.
Here, we are using flipud() method of numpy to reverse a numpy array. flipud method returns numpy array object.
Below is the Python code given:
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# import numpy module import numpy as np # numpy array arr = np.array([10, 20, 30, 40, 50, 60]) print("Original array is:", arr) # reverse an array using slicing rev_arr = np.flipud(arr) print("Reversed array is:", rev_arr) |
Output:
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Original array is: [10 20 30 40 50 60] Reversed array is: [60 50 40 30 20 10] |
Print array in reverse order
You can loop through the array in reverse order. Loop will start from array.lenght -1 and end at 0 by step value of 1.
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#Initialize array arrInt = [1, 2, 3, 4, 5]; print("Original array: "); for i in range(0, len(arrInt)): print(arrInt[i],end=' '), print("\nArray in reverse order: "); # Print array in reverse order for i in range(len(arrInt)-1, -1, -1): print(arrInt[i],end=' ') |
Output:
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Original array: 1 2 3 4 5 Array in reverse order: 5 4 3 2 1 |
That’s all about how to reverse array in Python.
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