# Append to empty numpy array – Python : Create an Empty 2D Numpy Array and Append Rows or Columns to it

## Create an empty 2-D NumPy array and append rows and columns

Append to empty numpy array: In this article, we will discuss what is a NumPy array, how to create a NumPy array in python, and how to append rows and columns to the empty NumPy array. First, let see what a NumPy array is and how we can create it. You can also create empty numpy array

### NumPy

Numpy create empty array and append: NumPy is a library in python that is created to work efficiently with arrays in python. It is fast, easy to learn, and provides efficient storage. It also provides a better way of handling data for the process. We can create an n-dimensional array in NumPy. To use NumPy simply have to import it in our program and then we can easily use the functionality of NumPy in our program. Let us see how NumPy works with the help of an example.

import numpy as np

#0-D array
arr = np.array(1)
print(arr)
print(type(arr))
print()

#1-D array
arr_1d = np.array([1, 2, 3, 4, 5])
print(arr_1d)
print(type(arr_1d))
print()

#2-D array
arr_2d = np.array([[1, 2, 3], [4, 5, 6]])
print(arr_2d)
print(type(arr_2d))


Output

1
<class 'numpy.ndarray'>

[1 2 3 4 5]
<class 'numpy.ndarray'>

[[1 2 3]
[4 5 6]]
<class 'numpy.ndarray'>

Here we see how we can easily work with an n-dimensional array in python using NumPy.

Let us come to the main topic of the article i.e how to create an empty 2-D array and append rows and columns to it.

### Create an empty NumPy array

Create empty numpy array and append: To create an empty array there is an inbuilt function in NumPy through which we can easily create an empty array. The function here we are talking about is the .empty() function.

Syntax: numpy.empty(shape, dtype=float, order=‘C’)

It accepts shape and data type as arguments. Then returns a new array of given shapes and data types. Let us understand this with the help of an example.

array = np.empty((0, 4), int)
print(array)
print(type(array))

Output

[]
<class 'numpy.ndarray'>

This is the NumPy array consisting of 0 rows and 4 columns.

Now we understand how to create an empty 2-D NumPy array, now let us see how to append rows and columns to this empty array.

As we want to append rows and columns so there is also an inbuilt functioning NumPy to done this task and the method name is .append().

Syntax: numpy.append(arr, values, axis=None)

It contains 3 parameters. First is arr in which we have to pass our NumPy array, second is values i.e. what values we want to be appended in our NumPy array and 3rd is the axis. Axis along which values need to be appended. To append as row axis is 0, whereas to append as column it is 1.

### Append rows to empty NumPy array

Numpy empty array append: With the help of the append() method, we can be done this task but we need to take care of some points before using the append function.

1.  As we append data row-wise so we need to pass axis=0.
2. We have to pass the row to be appended as the same shape of the numpy array otherwise we can get an error i.e. as we have created an empty array with 4 columns so now we are restricted to use 4 elements in our NumPy array otherwise we will get an error.

Let us see how this function works with the help of an example.

array = np.empty((0, 4), int)
array = np.append(array, np.array([[1,2,3,4], [5,6,7,8]]), axis=0)
print(array)
type(array)

Output

[[1 2 3 4]
[5 6 7 8]]
numpy.ndarray

Here we see with the help of append() we easily append rows in our empty 2-D NumPy array.

### Append columns to empty NumPy array

Empty 2d array python: With the help of the append() method, we can be done this task but here also we need to take care of some points before using the append function.

1.  As we append data column-wise so we need to pass axis=1.
2. We have to pass the column to be appended as the same shape of the numpy array otherwise we can get an error.

Let us see how this function works with the help of an example.

# Create an empty 2D numpy array with 4 rows and 0 column
array = np.empty((4, 0), int)

columns = np.array([[1,2,3,4], [5,6,7,8]])
array = np.append(array, columns.transpose(), axis=1)
print(array)

Output

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

Here we see with the help of the append method how we are able to append columns to our empty 2-D NumPy array. In this example or method, we see that we use the transpose() function. So let us understand why the transpose() function is used here.

### transpose() Function

Here transpose() has the same functionality that the transpose of a matrix in mathematics. Here we see that we create our array row-wise but we want to enter them in the .append() function column-wise. Hence transpose is used to swap rows and columns.