Course Content
NumPy in a Nutshell
NumPy in a Nutshell
Access Array Elements
In both lists and arrays, elements are accessed using square brackets. Let's review the distinction between indexing and slicing:
- To retrieve a single element, you simply need to specify the index of that element in square brackets (start counting from 0);
- If you want to obtain a sequence from the original array, you should use slices.
We'll start with simple indexing. Let's have a look at the following image:
Let's see how it works with examples.
Get the first element from the following array:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Get the first element print(arr[0])
Retrieve the second element from the following array:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Get the second element print(arr[1])
Retrieve the third and fourth elements from the following array and then add them together:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Adding the third and the fourth elements print(arr[2] + arr[3])
Now, it's time to explore slicing. First, let's examine the syntax of slicing: array[start:end:step]
, where:
start
is the index from which slicing begins;end
is the index where slicing stops (note that this index is not included);step
is the parameter that specifies the intervals between the indices.
Let's have a look at the following image:
Omitting start, end and step
As you can see, we can often omit the start
, end
, step
or even all of them at the same time. step
, for example, can be omitted when we want it to be equal to 1. start
and end
can be omitted in the following scenarios:
- Omitting
start
:- slicing from the first element (
step
is positive); - slicing from the last element (
step
is negative).
- slicing from the first element (
- Omitting
end
:- slicing to the last element inclusive (
step
is positive); - slicing to the first element inclusive (
step
is negative).
- slicing to the last element inclusive (
In the example above, a[2:4]
has the step
equal to 1. a[-2:]
goes from the second to last element to the end of the array with step
equal to 1. a[::2]
goes from the first element to the end of the array with step
equal to 2.
It's time to practice.
Task
Retrieve the first and last elements from the following array [13, 99, 11, 23, 5, 41]
and then multiply them. Please use positive indexing.
Thanks for your feedback!
Access Array Elements
In both lists and arrays, elements are accessed using square brackets. Let's review the distinction between indexing and slicing:
- To retrieve a single element, you simply need to specify the index of that element in square brackets (start counting from 0);
- If you want to obtain a sequence from the original array, you should use slices.
We'll start with simple indexing. Let's have a look at the following image:
Let's see how it works with examples.
Get the first element from the following array:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Get the first element print(arr[0])
Retrieve the second element from the following array:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Get the second element print(arr[1])
Retrieve the third and fourth elements from the following array and then add them together:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Adding the third and the fourth elements print(arr[2] + arr[3])
Now, it's time to explore slicing. First, let's examine the syntax of slicing: array[start:end:step]
, where:
start
is the index from which slicing begins;end
is the index where slicing stops (note that this index is not included);step
is the parameter that specifies the intervals between the indices.
Let's have a look at the following image:
Omitting start, end and step
As you can see, we can often omit the start
, end
, step
or even all of them at the same time. step
, for example, can be omitted when we want it to be equal to 1. start
and end
can be omitted in the following scenarios:
- Omitting
start
:- slicing from the first element (
step
is positive); - slicing from the last element (
step
is negative).
- slicing from the first element (
- Omitting
end
:- slicing to the last element inclusive (
step
is positive); - slicing to the first element inclusive (
step
is negative).
- slicing to the last element inclusive (
In the example above, a[2:4]
has the step
equal to 1. a[-2:]
goes from the second to last element to the end of the array with step
equal to 1. a[::2]
goes from the first element to the end of the array with step
equal to 2.
It's time to practice.
Task
Retrieve the first and last elements from the following array [13, 99, 11, 23, 5, 41]
and then multiply them. Please use positive indexing.
Thanks for your feedback!
Access Array Elements
In both lists and arrays, elements are accessed using square brackets. Let's review the distinction between indexing and slicing:
- To retrieve a single element, you simply need to specify the index of that element in square brackets (start counting from 0);
- If you want to obtain a sequence from the original array, you should use slices.
We'll start with simple indexing. Let's have a look at the following image:
Let's see how it works with examples.
Get the first element from the following array:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Get the first element print(arr[0])
Retrieve the second element from the following array:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Get the second element print(arr[1])
Retrieve the third and fourth elements from the following array and then add them together:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Adding the third and the fourth elements print(arr[2] + arr[3])
Now, it's time to explore slicing. First, let's examine the syntax of slicing: array[start:end:step]
, where:
start
is the index from which slicing begins;end
is the index where slicing stops (note that this index is not included);step
is the parameter that specifies the intervals between the indices.
Let's have a look at the following image:
Omitting start, end and step
As you can see, we can often omit the start
, end
, step
or even all of them at the same time. step
, for example, can be omitted when we want it to be equal to 1. start
and end
can be omitted in the following scenarios:
- Omitting
start
:- slicing from the first element (
step
is positive); - slicing from the last element (
step
is negative).
- slicing from the first element (
- Omitting
end
:- slicing to the last element inclusive (
step
is positive); - slicing to the first element inclusive (
step
is negative).
- slicing to the last element inclusive (
In the example above, a[2:4]
has the step
equal to 1. a[-2:]
goes from the second to last element to the end of the array with step
equal to 1. a[::2]
goes from the first element to the end of the array with step
equal to 2.
It's time to practice.
Task
Retrieve the first and last elements from the following array [13, 99, 11, 23, 5, 41]
and then multiply them. Please use positive indexing.
Thanks for your feedback!
In both lists and arrays, elements are accessed using square brackets. Let's review the distinction between indexing and slicing:
- To retrieve a single element, you simply need to specify the index of that element in square brackets (start counting from 0);
- If you want to obtain a sequence from the original array, you should use slices.
We'll start with simple indexing. Let's have a look at the following image:
Let's see how it works with examples.
Get the first element from the following array:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Get the first element print(arr[0])
Retrieve the second element from the following array:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Get the second element print(arr[1])
Retrieve the third and fourth elements from the following array and then add them together:
import numpy as np # Creating array arr = np.array([1, 2, 3, 4, 5]) # Adding the third and the fourth elements print(arr[2] + arr[3])
Now, it's time to explore slicing. First, let's examine the syntax of slicing: array[start:end:step]
, where:
start
is the index from which slicing begins;end
is the index where slicing stops (note that this index is not included);step
is the parameter that specifies the intervals between the indices.
Let's have a look at the following image:
Omitting start, end and step
As you can see, we can often omit the start
, end
, step
or even all of them at the same time. step
, for example, can be omitted when we want it to be equal to 1. start
and end
can be omitted in the following scenarios:
- Omitting
start
:- slicing from the first element (
step
is positive); - slicing from the last element (
step
is negative).
- slicing from the first element (
- Omitting
end
:- slicing to the last element inclusive (
step
is positive); - slicing to the first element inclusive (
step
is negative).
- slicing to the last element inclusive (
In the example above, a[2:4]
has the step
equal to 1. a[-2:]
goes from the second to last element to the end of the array with step
equal to 1. a[::2]
goes from the first element to the end of the array with step
equal to 2.
It's time to practice.
Task
Retrieve the first and last elements from the following array [13, 99, 11, 23, 5, 41]
and then multiply them. Please use positive indexing.