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Ultimate NumPy

Basic Indexing

Every NumPy array has elements and their respective indices. Here we will focus on indices in 1D arrays. Let's take a look at the following image:

Here we have an array of five elements: [9, 6, 4, 8, 10]. Every element has a positive and negative index. For example, 9 has 0 as its positive index and -5 as its negative index. As you can see, positive indexing in arrays starts at 0 and goes up to n-1, where n is the length of the array. Negative indexing, on the other hand, starts at -n and goes up to -1.

Accessing Elements by Indices

To access an element by its index, you should specify the index of this element in square brackets, e.g., array[2].

Note
If a specified index is out of bounds, an IndexError is thrown, so be cautious of that.

Let's take a look at an example:


              1234567891011121314
            
import numpy as np
array = np.array([9, 6, 4, 8, 10])
# Accessing the first element (positive index)
print(f'The first element (positive index): {array[0]}')
# Accessing the first element (negative index)
print(f'The first element (negative index): {array[-5]}')
# Accessing the last element (positive index)
print(f'The last element (positive index): {array[4]}')
# Accessing the last element (negative index)
print(f'The last element (negative index): {array[-1]}')
# Accessing the third element (positive index)
print(f'The third element (positive index): {array[2]}')
# Accessing the third element (negative index)
print(f'The third element (negative index): {array[-3]}')

As you can see, there is nothing complicated here.

Note
It is common practice to access the first element of the array using a positive index (0) and the last element using a negative index (-1).

Since the elements of our array are just numbers, we can perform all kinds of operations on them that we would do with regular numbers:


              1234
            
import numpy as np
array = np.array([9, 6, 4, 8, 10])
# Finding the average between the first and the last element
print((array[0] + array[-1]) / 2)

Here, we calculated the average of the first and the last elements of our array.

Завдання

Calculate the average of the first, fourth, and last elements:

Use a positive index to access the first element.
Use a positive index to access the fourth element.
Use a negative index to access the last element.
Calculate the average of these numbers.

Завдання

Calculate the average of the first, fourth, and last elements:

Use a positive index to access the first element.
Use a positive index to access the fourth element.
Use a negative index to access the last element.
Calculate the average of these numbers.

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Все було зрозуміло?

Секція 2. Розділ 1

Basic Indexing

Every NumPy array has elements and their respective indices. Here we will focus on indices in 1D arrays. Let's take a look at the following image:

Accessing Elements by Indices

To access an element by its index, you should specify the index of this element in square brackets, e.g., array[2].

Note
If a specified index is out of bounds, an IndexError is thrown, so be cautious of that.

Let's take a look at an example:


              1234567891011121314
            
import numpy as np
array = np.array([9, 6, 4, 8, 10])
# Accessing the first element (positive index)
print(f'The first element (positive index): {array[0]}')
# Accessing the first element (negative index)
print(f'The first element (negative index): {array[-5]}')
# Accessing the last element (positive index)
print(f'The last element (positive index): {array[4]}')
# Accessing the last element (negative index)
print(f'The last element (negative index): {array[-1]}')
# Accessing the third element (positive index)
print(f'The third element (positive index): {array[2]}')
# Accessing the third element (negative index)
print(f'The third element (negative index): {array[-3]}')

As you can see, there is nothing complicated here.

Note
It is common practice to access the first element of the array using a positive index (0) and the last element using a negative index (-1).

Since the elements of our array are just numbers, we can perform all kinds of operations on them that we would do with regular numbers:


              1234
            
import numpy as np
array = np.array([9, 6, 4, 8, 10])
# Finding the average between the first and the last element
print((array[0] + array[-1]) / 2)

Here, we calculated the average of the first and the last elements of our array.

Завдання

Calculate the average of the first, fourth, and last elements:

Use a positive index to access the first element.
Use a positive index to access the fourth element.
Use a negative index to access the last element.
Calculate the average of these numbers.

Завдання

Calculate the average of the first, fourth, and last elements:

Use a positive index to access the first element.
Use a positive index to access the fourth element.
Use a negative index to access the last element.
Calculate the average of these numbers.

Все було зрозуміло?

Секція 2. Розділ 1

Basic Indexing

Every NumPy array has elements and their respective indices. Here we will focus on indices in 1D arrays. Let's take a look at the following image:

Accessing Elements by Indices

To access an element by its index, you should specify the index of this element in square brackets, e.g., array[2].

Note
If a specified index is out of bounds, an IndexError is thrown, so be cautious of that.

Let's take a look at an example:


              1234567891011121314
            
import numpy as np
array = np.array([9, 6, 4, 8, 10])
# Accessing the first element (positive index)
print(f'The first element (positive index): {array[0]}')
# Accessing the first element (negative index)
print(f'The first element (negative index): {array[-5]}')
# Accessing the last element (positive index)
print(f'The last element (positive index): {array[4]}')
# Accessing the last element (negative index)
print(f'The last element (negative index): {array[-1]}')
# Accessing the third element (positive index)
print(f'The third element (positive index): {array[2]}')
# Accessing the third element (negative index)
print(f'The third element (negative index): {array[-3]}')

As you can see, there is nothing complicated here.

Note
It is common practice to access the first element of the array using a positive index (0) and the last element using a negative index (-1).

Since the elements of our array are just numbers, we can perform all kinds of operations on them that we would do with regular numbers:


              1234
            
import numpy as np
array = np.array([9, 6, 4, 8, 10])
# Finding the average between the first and the last element
print((array[0] + array[-1]) / 2)

Here, we calculated the average of the first and the last elements of our array.

Завдання

Calculate the average of the first, fourth, and last elements:

Use a positive index to access the first element.
Use a positive index to access the fourth element.
Use a negative index to access the last element.
Calculate the average of these numbers.

Завдання

Calculate the average of the first, fourth, and last elements:

Use a positive index to access the first element.
Use a positive index to access the fourth element.
Use a negative index to access the last element.
Calculate the average of these numbers.

Все було зрозуміло?

Every NumPy array has elements and their respective indices. Here we will focus on indices in 1D arrays. Let's take a look at the following image:

Accessing Elements by Indices

To access an element by its index, you should specify the index of this element in square brackets, e.g., array[2].

Note
If a specified index is out of bounds, an IndexError is thrown, so be cautious of that.

Let's take a look at an example:


              1234567891011121314
            
import numpy as np
array = np.array([9, 6, 4, 8, 10])
# Accessing the first element (positive index)
print(f'The first element (positive index): {array[0]}')
# Accessing the first element (negative index)
print(f'The first element (negative index): {array[-5]}')
# Accessing the last element (positive index)
print(f'The last element (positive index): {array[4]}')
# Accessing the last element (negative index)
print(f'The last element (negative index): {array[-1]}')
# Accessing the third element (positive index)
print(f'The third element (positive index): {array[2]}')
# Accessing the third element (negative index)
print(f'The third element (negative index): {array[-3]}')

As you can see, there is nothing complicated here.

Note
It is common practice to access the first element of the array using a positive index (0) and the last element using a negative index (-1).

Since the elements of our array are just numbers, we can perform all kinds of operations on them that we would do with regular numbers:


              1234
            
import numpy as np
array = np.array([9, 6, 4, 8, 10])
# Finding the average between the first and the last element
print((array[0] + array[-1]) / 2)

Here, we calculated the average of the first and the last elements of our array.

Завдання

Calculate the average of the first, fourth, and last elements:

Use a positive index to access the first element.
Use a positive index to access the fourth element.
Use a negative index to access the last element.
Calculate the average of these numbers.

Секція 2. Розділ 1