Numpy arrays are very versatile when it comes to manipulating and extracting values. In this tutorial, we will look at how to get the first column of a two-dimensional Numpy array with the help of some examples.

## Steps to get the first column of a Numpy Array

Let’s look at a step-by-step example of how to extract the first column from a two-dimensional Numpy array.

### Step 1 – Create a 2D Numpy array

First, we will create a 2D Numpy array that we will use throughout this tutorial.

import numpy as np # create 2D Numpy array ar = np.array([ [1, 2, 3], [4, 5, 6], [7, 8, 9] ]) # display the array print(ar)

Output:

[[1 2 3] [4 5 6] [7 8 9]]

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

function to create a two-dimensional Numpy array having three rows and three columns.

You can see that the first column of the above array contains the values 1, 4, and 7

### Step 2 – Slice the array to get the first column

You can use slicing to extract the first column of a Numpy array. The idea is to slice the original array for all the rows and just the first column (which has a column index of 0).

For example, to get the first column of the array `ar`

use the syntax `ar[:, 0]`

.

Let’s get the first column of the array created above.

# get the first column ar[:, 0]

Output:

array([1, 4, 7])

We get a Numpy array of the values in the first column of our original array (`ar`

). Note that the resulting array, here, is one-dimensional.

ar[:, 0].shape

Output:

(3,)

If you instead want the first column as a Numpy array with shape `(3, 1)`

(like a column vector) use the following syntax –

# get the first column ar[:, [0]]

Output:

array([[1], [4], [7]])

We get the first column from the original array as a separate column (sort of like a column vector). Let’s see its shape.

ar[:, [0]].shape

Output:

(3, 1)

You can see that the resulting array is of shape `(3, 1)`

## Summary

In this tutorial, we looked at how to extract the first column of a two-dimensional Numpy array. The following is a short summary of the steps mentioned in this tutorial.

- Create a 2D Numpy array (skip this step if you already have an array to operate on).
- Use slicing to get the first column of the array –
- If you want the values in the first column as a simple one-dimensional array, use the syntax
`ar[:, 0]`

. - If you want the resulting values in a column vector (for example, with shape
`(n, 1)`

where n is the total number of rows), use the syntax`ar[: [0]]`

.

- If you want the values in the first column as a simple one-dimensional array, use the syntax

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