np.ones() – Create 1D / 2D Numpy Array filled with ones (1’s)

In this article, we will discuss how to create 1D or 2D numpy arrays filled with ones (1s).

np.ones() – Create 1D / 2D Numpy Array filled with ones (1’s)

numpy.ones()

Python’s Numpy module provides a function to create a numpy array of given shape & type and filled with 1’s i.e,

numpy.ones(shape, dtype=float, order='C')

Arguments:

  • shape: Shape of the numpy array. Single integer or sequence of integers.
  • dtype: (Optional) Data type of elements. Default is float64.
  • order: (Optional) Order in which data is stored in multi-dimension array i.e. in row major(‘F’) or column major (‘C’). Default is ‘C’.

Returns:

  • It returns a numpy array of given shape but filled with ones.

Let’s understand with some examples but first we need to import the numpy module,

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import numpy as np

Create 1D Numpy Array of given length and filled with ones

Suppose we want to create a numpy array of five ones (1s). For that we need to call the numpy.ones() function with argument 5 i.e.

np.ones(5)

It returns a 1D numpy array with five 1s,

array([1., 1., 1., 1., 1.])

We can assign the array returned by ones() to a variable and print its type to confirm if it is a numpy array or not,

arr = np.ones(5)
print(arr)
print(type(arr))

Output:

[1. 1. 1. 1. 1.]
<class 'numpy.ndarray'>

Create Numpy array with ones of integer data type

By default numpy.ones() returns a numpy array of float ones. But if we want to create a numpy array of ones as integers, then we can pass the data type too in the ones() function. For example,

arr = np.ones(5, dtype=np.int64)
print(arr)

Output:

[1 1 1 1 1]

It returned a numpy array of ones as integers because we pass the datatype as np.int64.

Create two dimensional (2D) Numpy Array of ones

To create a multidimensional numpy array filled with ones, we can pass a sequence of integers as the argument in ones() function. For example, to create a 2D numpy array or matrix of 4 rows and 5 columns filled with ones, pass (4, 5) as argument in the ones() function.

arr_2d = np.ones( (4, 5) , dtype=np.int64)
print(arr_2d)

Output:

[[1 1 1 1 1]
 [1 1 1 1 1]
 [1 1 1 1 1]
 [1 1 1 1 1]]

It returned a matrix or 2D Numpy Array of 4 rows and 5 columns filled with 1s.

Create 3D Numpy Array filled with ones

To create a 3D Numpy array filled with ones, pass the dimensions as the argument in ones() function. For example,

arr_3d = np.ones( (2, 4, 5) , dtype=np.int64)
print(arr_3d)

Output:

[[[1 1 1 1 1]
  [1 1 1 1 1]
  [1 1 1 1 1]
  [1 1 1 1 1]]

 [[1 1 1 1 1]
  [1 1 1 1 1]
  [1 1 1 1 1]
  [1 1 1 1 1]]]

It created a 3D Numpy array of shape (2, 4, 5) filled with 1s.

Summary:

In this article we learned how to create 1D or 2D numpy array of given shape and filled with ones.

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