Extract the First N Elements of Numpy Array

The Numpy library in Python comes with a number of useful methods and techniques to work with and manipulate data in arrays. In this tutorial, we will look at how to get the first N elements of a one-dimensional Numpy Array with the help of some examples.

How to get the first n elements of a Numpy array?

To get the first n elements of a Numpy array, slice the array from index 0 to index n. The following is the syntax –

# first n elements of numpy array
ar[:n]

This will give us the elements in the array starting from the element at index 0 up to (but not including) the element at index n.

Steps to get the first n elements in an array

Let’s now look at a step-by-step example of using the above syntax on a Numpy array.

Step 1 – Create a Numpy array

First, we will create a Numpy array that we’ll operate on.

import numpy as np

# create numpy array
ar = np.array([1, 5, 6, 3, 2, 4, 7])
# display the array 
print(ar)

Output:

[1 5 6 3 2 4 7]

Here, we used the numpy.array() function to create a one-dimensional Numpy array containing some numbers. There are seven elements in the array.

Step 2 – Slice the array to get the first n elements

To get the first n elements of the above array, slice the array starting from the first element (0th index) up to (but not including) the element with the index n.

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For example, let’s get the first 3 elements from the array that we created in step 1.

# get first 3 elements of the array
print(ar[0:3])

Output:

[1 5 6]

We get the first 3 elements of the array.

In the above code, you don’t need to explicitly specify 0 (since you’re slicing starting from the very first element of the array).

# get first 3 elements of the array
print(ar[:3])

Output:

[1 5 6]

We get the same result as above.

For more on slicing Numpy arrays, refer to its documentation.

Summary

In this tutorial, we looked at how to get the first n elements of a one-dimensional Numpy array using slicing. The following is a short summary of the steps mentioned in the tutorial.

Create a Numpy array (skip this step if you already have an array to operate on).
Slice the array from index 0 to index n to get the first n elements of the array.

Author

Piyush Raj

Piyush is a data professional passionate about using data to understand things better and make informed decisions. He has experience working as a Data Scientist in the consulting domain and holds an engineering degree from IIT Roorkee. His hobbies include watching cricket, reading, and working on side projects.

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