Python Data Science NumPy Creating Arrays

A NumPy ndarray object can be created by using the array() function.

Example 1:

Code

import numpy as np

arr = np.array([1, 2, 3, 4, 5, 6])

print(arr)

print(type(arr))

the output will be

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

type(): This built-in Python function tells us the type of the object passed to it. Like in above code it shows that arr is numpy.ndarray type.

To create an ndarray, we can pass a list, tuple or any array-like object into the array() method, and it will be converted into an ndarray.

Example 2: Use a tuple to create a NumPy array.

Code

import numpy as np

arr = np.array((1, 2, 3, 4, 5))

print(arr)

the output will be
[1 2 3 4 5]

Dimensions in Arrays: A dimension in arrays is one level of array depth (nested arrays).

nested arrays are arrays that have arrays as their elements.

0-D Arrays

0-D arrays, or Scalars, are the elements in an array. Each value in an array is a 0-D array.

Example 3: Create a 0-D array with value 41.

Code

import numpy as np

arr = np.array(41)

print(arr)

the output will be
41

1-D Arrays Or Uni-dimensional: An array that has 0-D arrays as its elements is called uni-dimensional or 1-D array.

These are the most common and basic arrays.

Example 4: Create a 1-D array containing the values 1,2,3,4

Code

import numpy as np

arr = np.array([1, 2, 3, 4])

print(arr)

the output will be
[1 2 3 4]

2-D Arrays: An array that has 1-D arrays as its elements is called a 2-D array.

These are often used to represent matrix or 2nd order tensors.

NumPy has a whole sub module dedicated towards matrix operations called numpy.mat

Example 5: Create a 2-D array containing two arrays with the values 1,2,3,4 and 5,6,7,8

Code

import numpy as np

arr = np.array([[1,2,3,4], [5,6,7,8]])

print(arr)

the output will be

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

3-D arrays: An array that has 2-D arrays (matrices) as its elements is called 3-D array.

These are often used to represent a 3rd order tensor.

Example 6: Create a 3-D array with two 2-D arrays, both containing two arrays with the values 8,9,10 and 11,12,13

Code

import numpy as np

arr = np.array([[[8,9,10], [11,12,13]], [[8,9,10], [11,12,13]]])

print(arr)

the output will be

    [[[ 8  9 10]
  [11 12 13]]

 [[ 8  9 10]
  [11 12 13]]]   
       
   

Check Number of Dimensions?

NumPy Arrays provides the ndim attribute that returns an integer that tells us how many dimensions the array has.

Example 7: Check how many dimensions the arrays has?

Code

import numpy as np

a = np.array(41)

b = np.array([1, 2, 3, 4])

c = np.array([[1,2,3,4], [5,6,7,8]])

d = np.array([[[8,9,10], [11,12,13]], [[8,9,10], [11,12,13]]])

print(a.ndim)

print(b.ndim)

print(c.ndim)

print(d.ndim)

the output will be

    0
    1
    2
    3  
       
   

Higher Dimensional Arrays: An array can have any number of dimensions.

When the array is created, you can define the number of dimensions by using the ndmin argument.

Example 8: Create an array with 5 dimensions and verify that it has 5 dimensions.

Code

import numpy as np

arr = np.array([1, 2, 3, 4,5], ndmin=6)

print(arr)

print('number of dimensions :', arr.ndim)

the output will be
[[[[[[1 2 3 4 5]]]]]]
number of dimensions : 6

In this array the innermost dimension (5th dim) has 4 elements, the 4th dim has 1 element that is the vector, the 3rd dim has 1 element that is the matrix with the vector, the 2nd dim has 1 element that is 3D array and 1st dim has 1 element that is a 4D array.