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How to add a new row to an empty NumPy array?
In this tutorial, we will learn how to add a new row to an empty NumPy array?
By Pranit Sharma Last updated : May 26, 2023
Problem Statement
Given an empty NumPy array, we have to add a new row in it i.e., write a Python program to add a new row to an empty NumPy array.
Adding a new row to an empty NumPy array
There are three common and efficient approaches for adding a new row to an empty NumPy array, using numpy.append(), numpy.hstack(), or numpy.r_. Let's discuss these approaches in detail.
1) Using numpy.append() Method
The numpy.append() appends values to the end of an array and it can also be used to add a new row in an empty NumPy array. You have to pass an empty array and an array with row values in it.
Syntax
arr = np.append(arr, np.array([90, 80, 70]))
Example 1
# Import numpy
import numpy as np
# Creating an empty numpy array
arr = np.array([])
# Display original array
print("Original array:\n", arr, "\n")
# Appending a new row to NumPy array
# using numpy.append() method
arr = np.append(arr, np.array([90, 80, 70]))
# Printing the updated array
print("Updated array:\n", arr)
Output
Original array:
[]
Updated array:
[90. 80. 70.]
2) Using numpy.hstack() Method
The numpy.hstack() stack arrays in sequence horizontally and it can also be used to add a new row in an empty NumPy array.
Syntax
arr = np.hstack((arr, np.array([90, 80, 70])))
Example 2
# Import numpy
import numpy as np
# Creating an empty numpy array
arr = np.array([])
# Display original array
print("Original array:\n", arr, "\n")
# Appending a new row to NumPy array
# using numpy.hstack() method
arr = np.hstack((arr, np.array([90, 80, 70])))
# Printing the updated array
print("Updated array:\n", arr)
Output
Original array:
[]
Updated array:
[90. 80. 70.]
3) Using numpy.r_
The numpy.r_ translates slice objects to concatenation along the first axis and it can also be used to add a new row in an empty NumPy array. You need to pass the empty array object and a new array with row values.
Syntax
arr = np.r_[arr, np.array([90, 80, 70])]
Example 3
# Import numpy
import numpy as np
# Creating an empty numpy array
arr = np.array([])
# Display original array
print("Original array:\n", arr, "\n")
# Appending a new row to NumPy array
# using numpy.r_
arr = np.r_[arr, np.array([90, 80, 70])]
# Printing the updated array
print("Updated array:\n", arr)
Output
Original array:
[]
Updated array:
[90. 80. 70.]
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