Appending values at the end of an NumPy array

Let us see how to append values at the end of a NumPy array. Adding values at the end of the array is a necessary task especially when the data is not fixed and is prone to change. For this task, we can use numpy.append() and numpy.concatenate(). This function can help us to append a single value as well as multiple values at the end of the array. In this article, we will also see how to append elements to the NumPy array.

Appending Values at the End of an NumPy Array

Below are the ways by which we can append values at the end of a NumPy Array in Python:

• Appending a Single Value to a 1D Array
• Appending Another Array at the End of a 1D Array
• Appending Values at the End Using Concatenation
• Appending with a Different Array Type
• Appending Using List Comprehension and numpy.concatenate
• Appending Values at the End of the N-Dimensional Array

Appending a Single Value to a 1D Array

For a 1D array, using the axis argument is not necessary as the array is flattened by default.

Output:

Original Array : [1 8 3 3 5]
Array after appending : [1 8 3 3 5 7]

Appending Another Array at the End of a 1D Array

You may pass a list or an array to the append function, the result will be the same.

Output:

First array is : [1 2 3]
Second array is : [4 5 6]
Array after appending : [1 2 3 4 5 6]

Appending Values at the End Using Concatenation

In this example, two 2D arrays, arr1 and arr2, are vertically stacked using np.concatenate() along the 0th axis, resulting in a combined 2D array.

Output:

[[1 2]
 [3 4]
 [5 6]]

Appending with a Different Array Type

In this example, a 1D integer array arr and a 1D float array arr_float are appended together using np.append(), resulting in an upcasted float array as the output.

Output:

[1. 2. 3. 4. 5.]

Appending Using List Comprehension and numpy.concatenate

In this example, multiple arrays, including arr and two arrays from values_to_append, are concatenated using list comprehension and np.concatenate(), producing a single combined array.

Output:

[1 2 3 4 5 6 7 8 9]

Appending Values at the End of the N-Dimensional Array

It is important that the dimensions of both the array matches otherwise it will give an error.

Output:

Original Array
[[ 1 2 3 4 5 6]
 [ 7 8 9 10 11 12]] 
Array to be appended column wise
[[ 5 6 7 8 9 10]]
Array after appending the values column wise
[[ 1 2 3 4 5 6]
 [ 7 8 9 10 11 12]
 [ 5 6 7 8 9 10]] 
Array to be appended row wise
[[1]
 [2]]
Array after appending the values row wise
[[ 1 2 3 4 5 6 1]
 [ 7 8 9 10 11 12 2]]