Arrays have a fixed size. You can't append to them. If you know the upper bounds of the array, you can preallocate the array with
np.empty((10, 10, 10))
For a 10x10x10 matrix. You can then keep 3 indices x,y,z to track the actual size you have. Eg, add a new element with:
matrix[x,y,z] = newElement
x += 1
Then when you're done, you can extract the submatrix with
finalMatrix = matrix[:x,:y,:z]
Top answer 1 of 2
15
Arrays have a fixed size. You can't append to them. If you know the upper bounds of the array, you can preallocate the array with
np.empty((10, 10, 10))
For a 10x10x10 matrix. You can then keep 3 indices x,y,z to track the actual size you have. Eg, add a new element with:
matrix[x,y,z] = newElement
x += 1
Then when you're done, you can extract the submatrix with
finalMatrix = matrix[:x,:y,:z]
2 of 2
0
You can use np.empty((x,y,z))
You can find a good explanation in this answer: How to create 3 dimensions matrix in numpy , like matlab a(:,:,:)
TutorialsPoint
tutorialspoint.com › return-a-new-three-dimensional-array-without-initializing-entries-in-numpy
Return a new Three-Dimensional array without initializing entries in Numpy
import numpy as np # To return a new 3D array without initializing entries, use the numpy.empty() method in Python Numpy # The 1st parameter is the Shape of the empty array arr = np.empty([3, 3, 3]) # Display the array print("Array... ",arr) # Get the type of the array print(" Array type...
NumPy
numpy.org › doc › stable › reference › generated › numpy.empty.html
numpy.empty — NumPy v2.5 Manual
Array of uninitialized (arbitrary) data of the given shape, dtype, and order. Object arrays will be initialized to None. ... Return an empty array with shape and type of input.
NumPy
numpy.org › doc › 2.3 › reference › generated › numpy.empty.html
numpy.empty — NumPy v2.3 Manual
Array of uninitialized (arbitrary) data of the given shape, dtype, and order. Object arrays will be initialized to None. ... Return an empty array with shape and type of input.
Appdividend
appdividend.com › create-and-check-if-a-numpy-array-is-empty
How to Create and Check If a Numpy Array is Empty
July 10, 2025 - The easiest and most robust way to check if a numpy 1d, 2d, 3d, or multi-dimensional array is empty using np.ndarray.size attribute.
NumPy
numpy.org › devdocs › reference › generated › numpy.empty.html
numpy.empty — NumPy v2.6.dev0 Manual
Array of uninitialized (arbitrary) data of the given shape, dtype, and order. Object arrays will be initialized to None. ... Return an empty array with shape and type of input.
NumPy
numpy.org › doc › 1.25 › reference › generated › numpy.empty.html
numpy.empty — NumPy v1.25 Manual
Array of uninitialized (arbitrary) data of the given shape, dtype, and order. Object arrays will be initialized to None. ... Return an empty array with shape and type of input.
Top answer 1 of 3
2
I'd suggest using np.full_like to choose the fill-value directly...
x = np.full_like((3, 1), None, dtype=object)
... of course the dtype you chose kind of defines what you mean by "empty"
2 of 3
1
I am guessing that by empty, you mean an array filled with zeros.
Use np.zeros() to create an array with zeros. np.empty() just allocates the array, so the numbers in there are garbage. It is provided as a way to even reduce the cost of setting the values to zero. But it is generally safer to use np.zeros().
GeeksforGeeks
geeksforgeeks.org › numpy › how-to-create-an-empty-and-a-full-numpy-array
How to create an empty and a full NumPy array - GeeksforGeeks
September 19, 2025 - Use np.empty() function. Specify the shape of the array as a tuple.
SciPy
docs.scipy.org › doc › numpy-1.13.0 › reference › generated › numpy.empty.html
numpy.empty — NumPy v1.13 Manual
Return a new array of given shape and type, without initializing entries. ... empty, unlike zeros, does not set the array values to zero, and may therefore be marginally faster.
Data Science Dojo
discuss.datasciencedojo.com › python
Initializing a 3D Numpy array with random values in Python - Python - Data Science Dojo Discussions
January 30, 2023 - In the realm of data science and computational tasks, 3D Numpy arrays are a vital tool for managing multi-dimensional data. This thread explores the different techniques of initializing these arrays with random values, along with example codes. 1. Using the np.empty function: 2. Using the np.zeros function: 3. Using the np.random.random_sample function: All these methods will create a 3-dimensional NumPy array of shape (3, 4, 5) and fill it with random values in the range [0, 1).
NumPy
numpy.org › doc › 2.2 › reference › generated › numpy.empty.html
numpy.empty — NumPy v2.2 Manual
Array of uninitialized (arbitrary) data of the given shape, dtype, and order. Object arrays will be initialized to None. ... Return an empty array with shape and type of input.
Note.nkmk.me
note.nkmk.me › home › python › numpy
NumPy: Create an empty array (np.empty, np.empty_like) | note.nkmk.me
January 22, 2024 - The NumPy version used in this article is as follows. Note that functionality may vary between versions. ... To create an empty array specifying shape and data type (dtype), use np.empty().
w3resource
w3resource.com › numpy › array-creation › empty.php
NumPy: numpy.empty() function - w3resource
We should use numpy.empty() when we need to create an array of a specific shape and type but do not require the elements to be initialized to any particular value, which can save time when dealing with large arrays.
NumPy
numpy.org › doc › 2.1 › reference › generated › numpy.empty.html
numpy.empty — NumPy v2.1 Manual
Array of uninitialized (arbitrary) data of the given shape, dtype, and order. Object arrays will be initialized to None. ... Return an empty array with shape and type of input.
Educative
educative.io › answers › how-to-create-an-empty-numpy-array
How to create an empty NumPy array
numpy.zeros(shape, dtype=float, order='C') numpy.empty(shape, dtype=float, order='C') # Shape -> Shape of the new array, e.g., (2, 3) or 2. # dtype -> The desired data-type for the array,e.g., numpy.int8. Default is numpy.float64. This parameter is optional. # order -> Indicates whether multi-dimensional data should be stored in row-major (C-style) or column-major (Fortran-style) order in memory.
NumPy
numpy.org › doc › 1.18 › reference › generated › numpy.empty.html
numpy.empty — NumPy v1.18 Manual
May 24, 2020 - Array of uninitialized (arbitrary) data of the given shape, dtype, and order. Object arrays will be initialized to None. ... Return an empty array with shape and type of input.
TutorialsPoint
tutorialspoint.com › numpy › numpy_empty_function.htm
Numpy empty() Function
We can create an n-dimensional NumPy array by passing a tuple of two numeric values as an argument to the numpy.empty() function.
NumPy
numpy.org › doc › 2.4 › reference › generated › numpy.empty.html
numpy.empty — NumPy v2.4 Manual
Array of uninitialized (arbitrary) data of the given shape, dtype, and order. Object arrays will be initialized to None. ... Return an empty array with shape and type of input.
Python Guides
pythonguides.com › python-numpy-empty-array
Create An Empty Array Using NumPy In Python
May 7, 2025 - NumPy arrays have a fixed size. np.append cannot extend one, so it allocates a brand new array and copies everything across, every single iteration. Build a plain Python list and convert once at the end. Lists over-allocate, so appending to them is cheap. If you know the final length in advance, allocate with np.empty(n) up front and assign by index.