Arrays in python

Arrays
 Array is basically a data structure which can hold more than one value at a time.
 It is a collection or ordered series of items at same time
 Each item stored in an array is called an element.
 Each location of an element in an array has a numerical index, which is used to
identify the element.
 Format: array_name = array(‘type_code’,[initializer])

Type Code
Typecode Value
b Represents signed integer of size 1
byte/td>
B Represents unsigned integer of size 1
byte
c Represents character of size 1 byte
i Represents signed integer of size 2
bytes
I Represents unsigned integer of size 2
bytes
f Represents floating point of size 4
bytes
d Represents floating point of size 8
bytes

 Arrays in Python can be created after importing the array module
 There are three methods to import array library
import array
Import array as arr
from array import *
How to create an Arrays in Python

Accessing Array Element
 Accessing elements using index value
 Index starts from 0 to n-1where n is the number of elements
 -ive index value can be used as well, -ive indexing starts from reverse order
0 1 2 3 4 5

Example
import array as arr
a = arr.array('i', [2, 4, 6, 8])
print("First element:", a[0])
print("Second element:", a[1])
print("last element:", a[-1])
Output
First element is: 2
Second element: 4
last element: 8

Basic Array Operations
 Finding the length of an array
 Adding/Changing element of an array
 Removing/deleting element of an array
 Array concatenation
 Slicing
 Looping through an array
 sorting

Finding the length of an array
 Number of element present in the array
 Using len() function to find the length
 The len() function returns an integer value that is equal to the number of elements
present in that array

Finding the length of an array
 Syntax
 Example
from array import *
a = array('i', [2, 4, 6, 8])
print(len(a)) output
4
len(array_name)

Adding elements to an array
 Using functions to add elements
 append() is used to add a single element at the end of an array
 extend() is used to add a more than one element at the end of an array
 insert() is used to add an element at the specific position in an array

Example
from array import *
numbers = array('i', [1, 2, 3])
numbers.append(4)
print(numbers)
numbers.extend([5, 6, 7])
print(numbers)
numbers.insert(3,8)
print(numbers)

 Output
array('i', [1, 2, 3, 4])
array('i', [1, 2, 3, 4, 5, 6, 7])
array('i', [1, 2, 3, 8, 4, 5, 6, 7])

Removing elements of an array
 Functions used to removing elements of an array
 pop() is used when we want to remove an element and return it.
 remove() is used when we want to remove an element with a specific value
without returning it.

Example
import array as arr
numbers = arr.array('i', [10, 11, 12, 12, 13])
numbers.remove(12)
print(numbers) # Output: array('i', [10, 11, 12, 13])
numbers.pop(2) # Output: 12
print(numbers)

Arrays Concatenation
 Arrays concatenation is done using + sign
 Example
import array as n
a = n.array('i', [10, 11, 12, 12, 13])
b = n.array('i', [21, 22, 35, 26,39])
c=a+b
print(c) output
array('i', [10, 11, 12, 12, 13, 21, 22, 35, 26, 39])

Slicing an array
 An array can be sliced using the : symbol
 This returns a range of elements that we have specified by the index number
 Example
import array as arr
numbers_list = [2, 5, 62, 5, 42, 52, 48, 5]
numbers_array = arr.array('i', numbers_list)
print(numbers_array[2:5]) # 3rd to 5th
print(numbers_array[:-5]) # beginning to 5th
print(numbers_array[5:]) # 6th to end
print(numbers_array[:]) # beginning to end

Looping through an array
 For loop used to iterates over the items of an array specified number of
times
 While loop iterates the elements until a certain condition is met
 Example
from array import *
numbers_list = [2, 5, 62, 5, 42, 52, 48, ]
a = array('i', numbers_list)
for x in a:
print(x)

Sorting of an array
 sort the elements of the array in ascending order
 Use sorted() buit in function to sort the array
 Format: sorted(array_name)

Example
from array import *
a = array('i',[4,3,6,2,1])
b=sorted(a)
for x in b:
print(x)
Output:
1
2
3
4
6

Sorting of array in descending order
 Format: sorted(array_name, reverse=true)
 Example:
from array import * output:
a = array('i',[4,3,6,2,1]) 6
b=sorted(a, reverse=true) 4
for x in b: 3
print(x) 2
1

Array Methods
 Python has a set of built-in methods that you can use on lists/arrays.
Method Description
append() Adds an element at the end of the list
clear() Removes all the elements from the list
copy() Returns a copy of the list
count() Returns the number of elements with the specified value
extend() Add the elements of a list (or any iterable), to the end of the
current list
index() Returns the index of the first element with the specified value
insert() Adds an element at the specified position
pop() Removes the element at the specified position
remove() Removes the first item with the specified value
reverse() Reverses the order of the list
sort() Sorts the list

TYPES OF ARRAYS
 As we know that arrays are of 3 types which include
 1D Array
 2D Array
 Multi D Array
In python we use
Package Numpy
We have to install it using python tools(PIP)
First of all import library that is numpy as np

Import numpy
 There are three methods to import numpy
import numpy
import numpy as np
from numpy import *

Example 1 D Array
# 1D Array
Import numpy as np
a = np.array([10,20,30,40,50])
print (a)
 Output
array([10,20,30,40,50])

Example 2D Array
Import numpy as np
#2D Array
#3x3 Array
B=np.array([
[10,20,30,],
[40,50,60],
[70,80,90]])
print (b)

Example 3D Array
Import numpy as np
# 3D Array
# 3x3x3
C=np.array([
[[1,2,3],[4,5,6],[7,8,9]],
[[9,8,7],[6,5,4],[3,2,1]],
[[1,2,3],[4,5,6],[7,8,9]]
])
Print (c)

Arrays in python

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