How to set the size of an array in python

Hey, folks! In this article, we will be focusing on some Easy Ways to Initialize a Python Array.

What is a Python array?

Python Array is a data structure that holds similar data values at contiguous memory locations.

When compared to a List(dynamic Arrays), Python Arrays stores the similar type of elements in it. While a Python List can store elements belonging to different data types in it.

Now, let us look at the different ways to initialize an array in Python.

Method 1: Using for loop and Python range() function

Python for loop and range() function together can be used to initialize an array with a default value.

Syntax:

[value for element in range(num)]

Python range() function accepts a number as argument and returns a sequence of numbers which starts from 0 and ends by the specified number, incrementing by 1 each time.

Python for loop would place 0(default-value) for every element in the array between the range specified in the range() function.

Example:

arr=[]
arr = [0 for i in range(5)] 
print(arr)

We have created an array — ‘arr’ and initalized it with 5 elements carrying a default value (0).

Output:

Method 2: Python NumPy module to create and initialize array

Python NumPy module can be used to create arrays and manipulate the data in it efficiently. The numpy.empty() function creates an array of a specified size with a default value = ‘None’.

Syntax:

numpy.empty(size,dtype=object)

Example:

import numpy as np
arr = np.empty(10, dtype=object) 
print(arr)

Output:

[None None None None None None None None None None]

Method 3: Direct method to initialize a Python array

While declaring the array, we can initialize the data values using the below command:

array-name = [default-value]*size

Example:

arr_num = [0] * 5
print(arr_num)

arr_str = ['P'] * 10
print(arr_str)

As seen in the above example, we have created two arrays with the default values as ‘0’ and ‘P’ along with the specified size with it.

Output:

[0, 0, 0, 0, 0]
['P', 'P', 'P', 'P', 'P', 'P', 'P', 'P', 'P', 'P']

Conclusion

By this, we have come to the end of this topic. Please feel free to comment below in case, you come across any doubt.

References

• Python array initialization — Documentation

To change the size of an array in Python, use the reshape method of the numpy library.

reshape(a,d)

• The first parameter (a) is the name of the array (vector or matrix) to be transformed.
• The second parameter (d) is a number or a tuple indicating the number of rows and columns of the new array.

The reshape function changes the size of the array without deleting the elements.

Note. The new size must equal the cardinality of the old array. For example, if a vector has 10 elements, it can be transformed into a 5x2 or 2x5 matrix. It cannot be made into a 3x3 matrix or anything else.

Example

Example 1 (vector to matrix)

Create an array of 10 elements using the array method.

import numpy as np
x=np.array([1,2,3,4,5,6,7,8,9,10])

The new array x has one size. It is a vector.

Change the array to a 5x2 array using the function reshape.

y=np.reshape(x,[5,2])

The new array y has two dimensions.

>>> y
array([[ 1, 2],
[ 3, 4],
[ 5, 6],
[ 7, 8],
[ 9, 10]])

It has the same elements as the vector x but arranged in a matrix.

Example 2

To get the same result, use reshape as the method.

y=x.reshape([5,2])

The end result is the same.

Example 3 (from matrix to vector)

Create a 2x5 matrix

import numpy as np
x=np.array([[1,2,3,4,5],[6,7,8,9,10]])

The array x has two dimensions

>>> x
array([[ 1, 2, 3, 4, 5],
[ 6, 7, 8, 9, 10]])

Transform the matrix into a vector.

z=np.reshape(x,10)

The new array has one size.

>>> z
array([ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10])

https://how.okpedia.org/en/python/how-to-change-array-size-in-python