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initialize a numpy array [duplicate]

stackoverflow.com › questions › 4535374 › initialize-a-numpy-array

numpy.zeros

Return a new array of given shape and type, filled with zeros.

or

numpy.ones

Return a new array of given shape and type, filled with ones.

or

numpy.empty

Return a new array of given shape and type, without initializing entries.

However, the mentality in which we construct an array by appending elements to a list is not much used in numpy, because it's less efficient (numpy datatypes are much closer to the underlying C arrays). Instead, you should preallocate the array to the size that you need it to be, and then fill in the rows. You can use numpy.append if you must, though.

Answer from Katriel on Stack Overflow

w3schools.com › python › numpy › numpy_creating_arrays.asp

NumPy Creating Arrays

The array object in NumPy is called ndarray. We can create a NumPy ndarray object by using the array() function.

numpy.org › doc › 2.5 › user › basics.creation.html

Array creation — NumPy v2.5 Manual

In the third example, the array is dtype=np.float64 to accommodate the step size of 0.1. Due to roundoff error, the stop value is sometimes included. numpy.linspace will create arrays with a specified number of elements, and spaced equally between the specified beginning and end values.

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stackoverflow.com › questions › 4535374 › initialize-a-numpy-array

python - initialize a numpy array - Stack Overflow

numpy.zeros

Return a new array of given shape and type, filled with zeros.

or

numpy.ones

Return a new array of given shape and type, filled with ones.

or

numpy.empty

Return a new array of given shape and type, without initializing entries.

However, the mentality in which we construct an array by appending elements to a list is not much used in numpy, because it's less efficient (numpy datatypes are much closer to the underlying C arrays). Instead, you should preallocate the array to the size that you need it to be, and then fill in the rows. You can use numpy.append if you must, though.

The way I usually do that is by creating a regular list, then append my stuff into it, and finally transform the list to a numpy array as follows :

Use with AIimport numpy as np
big_array = [] #  empty regular list
for i in range(5):
    arr = i*np.ones((2,4)) # for instance
    big_array.append(arr)
big_np_array = np.array(big_array)  # transformed to a numpy array

of course your final object takes twice the space in the memory at the creation step, but appending on python list is very fast, and creation using np.array() also.

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numpy.org › doc › stable › reference › generated › numpy.array.html

numpy.array — NumPy v2.5 Manual

Create an array. ... An array, any object exposing the array interface, an object whose __array__ method returns an array, or any (nested) sequence. If object is a scalar, a 0-dimensional array containing object is returned. ... The desired data-type for the array. If not given, NumPy will try to use a default dtype that can represent the values (by applying promotion rules when necessary.)

geeksforgeeks.org › python › numpy-array-creation

Numpy - Array Creation - GeeksforGeeks

July 23, 2025 - Numpy Arrays are grid-like structures similar to lists in Python but optimized for numerical operations. The most straightforward way to create a NumPy array is by converting a regular Python list into an array using the np.array() function.

numpy.org › doc › stable › reference › routines.array-creation.html

Array creation routines — NumPy v2.5 Manual

Array creation · Note · Please refer to Record arrays for record arrays. Note · numpy.char is used to create character arrays.

apxml.com › courses › intermediate-python-programming-ml › chapter-2-numerical-computing-numpy › numpy-array-creation

NumPy Array Creation Methods

NumPy provides a rich set of functions for generating these arrays in various ways, catering to different needs in data analysis and machine learning. The most straightforward way to create a NumPy array is by converting existing Python sequence-like objects, such as lists or tuples, using the np.a...

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numpy.org › devdocs › reference › routines.array-creation.html

Array creation routines — NumPy v2.6.dev0 Manual

Array creation · Note · Please refer to Record arrays for record arrays. Note · numpy.char is used to create character arrays.

numpy.org › devdocs › user › basics.creation.html

Array creation — NumPy v2.6.dev0 Manual

In the third example, the array is dtype=np.float64 to accommodate the step size of 0.1. Due to roundoff error, the stop value is sometimes included. numpy.linspace will create arrays with a specified number of elements, and spaced equally between the specified beginning and end values.

geeksforgeeks.org › numpy › different-ways-to-create-numpy-arrays-in-python

Different Ways to Create Numpy Arrays in Python - GeeksforGeeks

January 31, 2026 - The simplest way to create a NumPy array is by passing a Python list or tuple to the numpy.array() function.

Python Like You Mean It

pythonlikeyoumeanit.com › Module3_IntroducingNumpy › FunctionsForCreatingNumpyArrays.html

Functions for Creating NumPy Arrays — Python Like You Mean It

You can create an array from a Python list or tuple by using NumPy’s array function. NumPy will interpret the structure of the data it receives to determine the dimensionality and shape of the array.

codecademy.com › article › numpy-arrays-guide

Creating and Using NumPy Arrays - A Complete Guide | Codecademy

Here’s a comparison of the most commonly used functions: Let’s explore each function with practical examples: The np.array() function is the most common way to create a NumPy array.

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Creating Numpy Array - YouTube

Python Playlist :- https://www.youtube.com/playlist?list=PLsyeobzWxl7poL9JTVyndKe62ieoN-MZ3Check out our courses:Mastering Agentic AI with Java: Spring AI, ...

Published: November 11, 2024

medium.com › @amit25173 › trick-to-quickly-numpy-create-array-with-same-value-5fac963d3921

Trick to Quickly numpy create array with same value | by Amit Yadav | Medium

April 12, 2025 - Can I create a multi-dimensional array filled with the same value? Absolutely! Just specify your desired shape in numpy.full(), and you'll have your multi-dimensional array all filled up.

medium.com › data-science › here-are-30-ways-that-will-make-you-a-pro-at-creating-numpy-arrays-932b77d9a1eb

Here Are 30 Ways That Will Make You a Pro at Creating NumPy Arrays | by Avi Chawla | TDS Archive | Medium

August 31, 2022 - For instance, the code block below demonstrates the creation of a 3-dimensional NumPy array from a list of lists of lists. You can also create a NumPy array from a list of strings using the np.array() method:

numpy.org › doc › 2.4 › reference › routines.array-creation.html

Array creation routines — NumPy v2.4 Manual

Array creation · Note · Please refer to Record arrays for record arrays. Note · numpy.char is used to create character arrays.

Towards Data Science

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Here Are 30 Ways That Will Make You a Pro at Creating NumPy Arrays | Towards Data Science

August 31, 2022 - The input does not necessarily have to be a Python List. You can also create a NumPy array from a Python Tuple using the [np.array()](https://numpy.org/doc/stable/reference/generated/numpy.array.html) method:

pp4rs.github.io › pp4rs-python › notebooks › numpy › 01-create_array.html

Numpy Basics - Creating Arrays — Python for Economics and Business Research

These are not the only data types NumPy can work with; and it’s important to know these types. Here’s a list of most data types that you will encounter: Source: Jake VanderPlas (2016), Python Data Science Handbook Essential Tools for Working with Data, O’Reilly Media. We often will not want to manually enter the contents of an array ourselves. It is more efficient to create arrays from scratch using routines built into NumPy.

openclassrooms.com › us › courses › 8253136-use-python-libraries-for-data-science › 8358218-create-your-first-arrays-using-numpy

Create Your First Arrays Using NumPy - OpenClassrooms

This is where the NumPy library comes in! The name is derived from Numerical Python and the library provides a set of functions to efficiently perform operations on data. It also provides an object that is at the heart of almost all Python data ecosystems: the array.

hyperskill.org › university › numpy › numpy-creating-arrays

NumPy Creating Arrays

September 4, 2024 - These functions are useful for creating arrays of a specific size filled with default values. The numpy.linspace() function generates evenly spaced values within a specified range.