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 columns of a two-dimensional Numpy Array with the help of some examples.

## How to get the first n columns of a 2D Numpy array?

You can use slicing to get the first N columns of a 2D array in Numpy. Here, we use column indices to specify the range of columns that we’d like to slice. To get the first n columns, use the following slicing syntax –

# first n columns of numpy array ar[:, :n]

It returns the first n columns (including all the rows) of the given array.

## Steps to get the first n columns of 2D array

Let’s now look at a step-by-step example of using the above syntax on a 2D Numpy array.

### Step 1 – Create a 2D Numpy array

First, we will create a 2D Numpy array that we’ll operate on.

import numpy as np # create a 2D array ar = np.array([ ['Tim', 181, 86], ['Peter', 170, 68], ['Isha', 158, 59], ['Rohan', 168, 81], ['Yuri', 171, 65], ['Emma', 166, 64], ['Michael', 175, 78], ['Jim', 190, 87], ['Pam', 168, 57], ['Dwight', 187, 84] ]) # display the array print(ar)

Output:

[['Tim' '181' '86'] ['Peter' '170' '68'] ['Isha' '158' '59'] ['Rohan' '168' '81'] ['Yuri' '171' '65'] ['Emma' '166' '64'] ['Michael' '175' '78'] ['Jim' '190' '87'] ['Pam' '168' '57'] ['Dwight' '187' '84']]

Here, we used the `numpy.array()`

function to create a 2D Numpy array with 10 rows and 3 columns. The array contains information on the height (in cm) and weight (in kg) of some employees in an office.

### Step 2 – Slice the array to get the first n columns

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

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For example, let’s get the first 2 columns from the array that we created in step 1.

# first 2 columns print(ar[:, 0:2])

Output:

[['Tim' '181'] ['Peter' '170'] ['Isha' '158'] ['Rohan' '168'] ['Yuri' '171'] ['Emma' '166'] ['Michael' '175'] ['Jim' '190'] ['Pam' '168'] ['Dwight' '187']]

We get the first 2 columns of the 2D array.

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

# first 2 columns print(ar[:, :2])

Output:

[['Tim' '181'] ['Peter' '170'] ['Isha' '158'] ['Rohan' '168'] ['Yuri' '171'] ['Emma' '166'] ['Michael' '175'] ['Jim' '190'] ['Pam' '168'] ['Dwight' '187']]

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 columns of a two-dimensional Numpy array using slicing. The following is a short summary of the steps mentioned in the tutorial.

- Create a 2D Numpy array (skip this step if you already have an array to operate on).
- Slice the array from the column with index 0 to the column with index n (but not including it) to get the first n columns of the array.

You might also be interested in –

- Numpy – Get Max Value in Array
- Get the Median of Numpy Array – (With Examples)
- Pandas – Select first n rows of a DataFrame

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