Contents

## NumPy – Access elements of array

To access elements of a numpy array, you can use indexing operator `[]`

.

The indexing operator takes an integer or a list of integers representing the indices of elements you want to access.

index starts with a value of 0 for first element, and increments by one for subsequent elements.

If arr is numpy array, then the following expression accesses the element at index=5.

`arr[5]`

If arr is numpy array, then the following expression accesses the elements from start index of 5 to a stop index of 10 (stop not included in the returned object).

`arr[5:10]`

We can also specify a step value, with the following syntax.

`arr[start:stop:step]`

If the array is multi-dimensional then we can specify the indices for as many dimensions as required.

`arr[index_1][index_2]`

Accessing a range of elements is called slicing, and please refer the tutorial – NumPy Array Slicing.

## Examples

### 1. Access element at index=5

In the following program, we take a numpy array (one dimensional), and access the element at index=5.

**Python Program**

```
import numpy as np
arr = np.array([1, 2, 4, 9, 16, 25, 36, 49, 64])
element = arr[5]
print(element)
```

Run **Output**

`25`

**Explanation**

```
[1, 2, 4, 9, 16, 25, 36, 49, 64] <- arr
0 1 2 3 4 5 6 7 8 <- indices
arr[5] is 25
```

### 2. Access elements from index=2 until index=6

In the following program, we take a numpy array (one dimensional), and access the elements from index=2 until index=6.

**Python Program**

```
import numpy as np
arr = np.array([1, 2, 4, 9, 16, 25, 36, 49, 64])
elements = arr[2:6]
print(elements)
```

Run **Output**

`[ 4 9 16 25]`

**Explanation**

```
[1, 2, 4, 9, 16, 25, 36, 49, 64] <- arr
0 1 2 3 4 5 6 7 8 <- indices
|--------------|
4, 9, 16, 25 <- arr[2:6]
```

### 3. Access elements from index=2 until index=8 in steps of 2

In the following program, we take a numpy array (one dimensional), and access the elements from index=2 until index=8 in steps of 2.

**Python Program**

```
import numpy as np
arr = np.array([1, 2, 4, 9, 16, 25, 36, 49, 64])
elements = arr[2:8:2]
print(elements)
```

Run **Output**

`[ 4 16 36]`

**Explanation**

```
[1, 2, 4, 9, 16, 25, 36, 49, 64] <- arr
0 1 2 3 4 5 6 7 8 <- indices
|- - - |
4, 16, 36 <- arr[2:8:2]
```

## Summary

In this tutorial of Python Examples, we learned how to access elements of a numpy array using indexing operator.