Python Program to get the first given number of items from the array

An array is a data structure of a set of items with the same data type, and each element is identified by an index.

Arrays in python

Python does not have its own data structure to represent an array. However, we can use the list data structure as an alternative to the arrays. Here we will use list an array −

[10, 4, 11, 76, 99]

Python provides some modules also which are more appropriate, and the modules are Numpy and array modules.

An integer array defined by using the array module is −

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

A Numpy array defined by the NumPy module is −

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

In this article, we will see how to get the first given number of items from an array.

Input Output Scenarios

Assume we have an input array with 9 integer values. And in the output, the first few items are accessed based on the specified number.

Input array:
[1, 2, 3, 4, 5, 6, 7, 8, 9]
Output:
[1, 2, 3]

The first 3 items 1, 2, 3 are accessed from the input array. Let’s take an array with all string elements.

Input array:
[‘a’, ‘b’, ‘c’, ‘d’, ‘e’]
Output:
[‘a’, ‘b’]

First 2items are retrieved from the input array. In the below examples, we will mainly use python slicing features to retrieve the first few elements.

Slicing

The slicing is used to access the group of elements from a sequence. Following is the syntax to perform slicing –

sequence_object[start : end]

Where,

• Start − The starting index where the slicing of the iterable starts. By default, it is 0.

• End − The ending index where the slicing of the iterable stops. The default value is the length of the iterable object. And this value is excluded.

Using List

We can use the list-slicing feature to access the first given number of items from an array.

Example

Let’s take an example and apply list slicing to access the first given number of elements.

# creating array
lst = [1, 2, 0, 4, 1, 2, 3, 8] 

print ("The original array is: ", lst) 
print() 
numOfItems = 4
# Get first number of elements
result = lst[:numOfItems]
print ("The first {} number of elements are: {}".format(numOfItems, result))

Output

The original array is:  [1, 2, 0, 4, 1, 2, 3, 8]
The first 4 number of elements are: [1, 2, 0, 4]

The first 4 elements are accessed from the given array using the lst[:numOfItems] syntax and those elements are stored in the result variable.

Example

In this example, we will try to access the exceeded number of elements from an array.

# creating array
lst = [1, 2, 0] 

print ("The original array is: ", lst) 
print() 
numOfItems = 4

# Get first number of elements
result = lst[:numOfItems]
print ("The first {} number of elements are: {}".format(numOfItems, result))

Output

The original array is:  [1, 2, 0]
The first 4 number of elements are: [1, 2, 0]

The requested number of items are more compared to the total number of items available in the array list. Instead of rising an error, the slicing object lst[:numOfItems] displayed the available elements only.

Using NumPy array

Like List, we can also use NumPy arrays to access the array elements.

Example

In this example, we will try to access the first 2 elements from a NumPy array using the array slicing feature.

import numpy

# creating array
numpy_array = numpy.array([1, 3, 5, 6, 2, 9, 8])

print ("The original array is: ", numpy_array) 
print() 

numOfItems = 2

# get first number of 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:  [1 3]

The first two elements 1,3 are accessed from the numpy array object.

Using array module

The array module is the python built-in module, which is used to define an array object using the array() method.

Example

In this example, we will create an integer 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', [2, 1])

The first 2 elements from the input array arr are stored in the result variable.