Python program to remove first item of given number from array

An array is a data structure used to store a set of elements of the same data type. Each element in the array is identified by an index value or key.

Arrays in Python

Python has no native array data structure. Instead, we can use List data structure to represent arrays.

[1, 2, 3, 4, 5]

We can also use arrays or the NumPy module to process arrays in Python. Arrays defined by the array module are -

array('i', [1, 2, 3, 4])

Numpy arrays defined by the NumPy module are -

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

Python indexing starts from 0. The indexes of all the above arrays start from 0 and end at (n-1).

Input and output scenarios

Suppose we have an integer array containing 5 elements. In the output array, the first few elements will be removed.

Input array:
[1, 2, 3, 4, 5]
Output:
[3, 4, 5]

The first 2 elements 1 and 2 will be deleted from the input array.

In this article, we will see how to remove the first given number of items from an array. Here we mainly use python slicing to remove elements.

Slices in Python

Slicing allows accessing multiple elements at once instead of using an index to access a single element.

grammar

iterable_obj[start:stop:step]

where,

• Start: The starting index at which object slicing begins. The default value is 0.

• End: The end index where the object slicing stops. The default value is len(object)-1.

• Step size: Increase the number of the starting index. The default value is 1.

Use list

We can use list slicing to remove the first given number of elements from an array.

Example

Let's take an example of applying list slicing to remove the first element in an array.

# creating array
lst = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 

print ("The original array is: ", lst) 
print() 
numOfItems = 4
# remove first elements
result = lst[numOfItems:]
print ("The array after removing the elements is: ", result) 

Output

The original array is:  [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
The array after removing the elements is:  [5, 6, 7, 8, 9, 10]

Remove the first 4 elements from the given array and store the resulting array in the result variable. In this example, the original array remains unchanged.

Example

By using the python del keyword and the slice object, we can delete elements of the array.

# creating array
lst = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] 
print ("The original array is: ", lst) 
print() 
numOfItems = 4

# remove first elements
del lst[:numOfItems]
print ("The array after removing the elements is: ", lst) 

Output

The original array is:  [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
The array after removing the elements is:  [5, 6, 7, 8, 9, 10]

Statement lst[:numOfItems] retrieves the first given number of items in the array, and the del keyword deletes these items/elements.

Using NumPy arrays

Using numpy module and slicing technique we can easily remove the number of items from an array.

Example

In this example, we will remove the first element from the numpy array.

import numpy
# creating array
numpy_array = numpy.array([1, 3, 5, 6, 2, 9, 8])
print ("The original array is: ", numpy_array) 
print() 
numOfItems = 3

# remove first elements
result = numpy_array[numOfItems:]
print ("The result is: ", result) 

Output

The original array is:  [1 3 5 6 2 9 8]

The result is:  [6 2 9 8]

We have successfully removed the first 2 elements from a numpy array using array slicing.

Using the array module

The array module in Python also supports indexing and slicing techniques to access elements.

Example

In this example, we will create an array using the array module.

import array
# creating array
arr = array.array('i', [2, 1, 4, 3, 6, 5, 8, 7])
print ("The original array is: ", arr) 
print() 

numOfItems = 2
# remove first elements
result = arr[numOfItems:]
print ("The result is: ", result) 

Output

The original array is:  array('i', [2, 1, 4, 3, 6, 5, 8, 7])
The result is:  array('i', [4, 3, 6, 5, 8, 7])

The resulting array has the first 2 elements removed from array arr, where array arr has not changed.

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