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Python for machine learning – Collections

Welcome to another post about python for machine learning. In this post we will see Collections in python. There are four collections in python

  1. List
  2. Tuple
  3. Set
  4. Dictionary

Let us discuss about them one by one

List

A list in python is a collection which is ordered and changeable. A basic list is shown below. Lists are defined by square brackets ” [ ] “

thislist = ["apple", "banana", "cherry"]
print(thislist)

The output of the program is

['apple', 'banana', 'cherry']

It is interesting to know how to retrieve the data in python

index and range of indexes

see how to access the element using index

thislist = ["apple", "banana", "cherry"]
print(thislist[1])

The output of the above program will be banana. list is indexed from 0

let us see range of indexes by using the same program

thislist = ["apple", "banana", "cherry", "orange", "kiwi", "melon", "mango"]
print(thislist[2:5])

The output of the above program will be [‘cherry’, ‘orange’, ‘kiwi’]

Since we are only covering some important topics in the post,You refer other websites for learning python completely. I am just focusing on the aspects that are needed for machine learning

Tuple

The second collection we are going to see is tuple. The major difference between list and tuple is that list is changeable and tuple is unchangeable but both are ordered.

In python,Tuples are defined by Curve brackets ” ( ) ” as shown below

thistuple = ("apple", "banana", "cherry")
print(thistuple)

The output of the program is same as the list

(‘apple’, ‘banana’, ‘cherry’)

We can use the same method as in list to access the elements in tuple.

Sets

Set is a collection in python which is unordered and unindexed. sets are defined by curly brackets ” { } “

Let us see a basic set program

thisset = {"apple", "banana", "cherry"}
print(thisset)

The output is the same as the tuple and list. Since sets are unindexed we cannot access the elements by index. So, we need to loop through the set to retrieve the elements. We will see a program to access the data in the set.

thisset = {"apple", "banana", "cherry"}

for x in thisset:
  print(x)

The output is

cherry
apple
banana

Dictionary

A dictionary is a unordered and indexed and changeable. Dictionary is written in python by same curly brackets ” { } ” but has keys and values.

We will see a basic program about dictionary

thisdict =	{
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict)

The output of the program is

{‘brand’: ‘Ford’, ‘model’: ‘Mustang’, ‘year’: 1964}

Now we shall see how to access data from dictionary

we can access the data in a dictionary using the associated key. The program below will demonstrate how to access the data.

x = thisdict["model"]

The output of the above program will be “Mustang”. How to change the data in a dictionary is as shown below:

thisdict["year"] = 2018

now the data in the dictionary will be changed and year value is changed to 2018.

We are not focusing on this much because we will be using numPy array and Pandas Dataframe for most of our tasks. So we won’t be using python list, tuple, sets, dictionaries. Since it is important to know these basics I’ve posted it.

In the next post we will see about numPy and what we can do with numPy.

Happy Coding

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Python for machine learning – Control Structures

Prerequisite for this course

In my previous posts, I forgot to mention this, the prerequisite for learning python for machine learning will be a basic understanding of basic programming concepts from any programming language like C, C++, Java etc.

In this post we will see the most important part of a programming language control structure

  1. Selection
    1. if
    2. if…else
    3. if….elif…else
  2. Repetition
    1. while
    2. for

Selection

used for making decisions in a program that branches the program in 2 or more ways let us see the selection statements in python and one example program for each statement. It will have the same logic as the other programming languages like C and C++

if – statement

The first selection statement we are going to look at is if statement, the basic syntax is the same as the other programming languages. Let us see the syntax of if statement in python

if (expression):
    statements

if you see the syntax of python you will notice there is no parenthesis ” { ” instead of parenthesis python uses ” : ” and indentation if you see the syntax the statement is indented to let python know that we are inside the if statement.

Other than the simple change the logic of if statement works as the same as the other programming languages. now let us see an example program with if statement.

a = 10
if a==10:
    print('it is ten')

the output will be “it is ten“

if…else – statement

The second selection statement is if…else statement if you look at the if…else statement we will see the syntax and basic program in python.

if (expression):
    statements
else:
    statements

Example program

a = 11
if a==10:
    print('it is ten')
else:
    print('it is not ten')

the output will be “it is not ten”

if…elif…else – statement

The third statement we are going to see is if…elif…else statement in python elseif is mentioned as elif that is why i am mentioning it as elif not as elseif. let us see the syntax of if…elif…else statement.

if (expression):
    statements
elif (expression):
    statements
else:
    statements

Now we will see the program.

a = 11
if a==10:
    print('it is ten')
elif a==11:
    print('it is eleven')
else:
    print('it is not ten')

the output will be “it is eleven”

Next we will see repetition statements

while – statement

The while statement functions as the same as in any other programming language we will see the syntax of while statement below.

while(expression):
    statements

We will see a example program

i = 1
while i < 6:
  print(i)
  i += 1

The above code will output ” 1 2 3 4 5 6 “.

for – statement

The next and last control statement we will see is for statement we will see the example below.

fruits = ["apple", "banana", "cherry"]
for x in fruits:
  print(x)

The output of the program is “apple banana cherry”

We will also see another basic program below.

for i in range(1,5):
    print(i)

The output will be ” 1 2 3 4″

That’s all for this post friends we will see Python collections in the next post

Happy Coding

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Python for machine learning: variables, datatypes

Contents

  1. Variables & Datatypes
  2. Basic program

Variables & Datatypes

Variables are basic building blocks of a programming language and it applies to python programs also. Variables hold data in memory. Python variables differ by a slight than the other programming languages. In python, variables can be declared without specifying the data type and the data type will be determined by the values assigned to the variable. for example in c++, declaring a variable “a” with the value assigned to it will be like the code below.

int a = 10;

But in python it is declared like

a = 10 #Assign the values 10 to variable a

Note : in python “;” is not need to end the statement

Let see more examples

x = 5         # assign variable x the value 5
y = x + 10     # assign variable y the value of x plus 10
z = y         # assign variable z the value of y

As with other programming languages, variables in python is case-sensitive and can include letter, number, ( _ ) char but the variable name cannot start with a number.

Let us see how python assigns the datatype based on the values by an example program.

x = 1
print(type(x)) # outputs: <class 'int'>

x = 1.0
print(type(x)) # outputs: <class 'float'>

if we see the first line 

x=1

we can see that it is a integer value and the output is displayed as

<class 'int'>

if we see the second variable declaration and ask it to print its type

x=1.0

we can see that it is a decimal number and its type is float

<class 'float'>

This applies to other data types too because python is a dynamically typed programming language and it assigns a data type to its variables based on the type of values assigned to it.

Basic Program

Let us see a basic program about declaring variables and datatypes.

x=10
y=x+12
print(y)
print("Data type of variable x and y" + str(type(x)) + str(type(y)))

d=1.2
print(d)
print("Data type of variable d is " + str(type(d)))

s = 'Arvin Education'
print(s)
print("Data type of variable s is " + str(type(s)))

The output is as follows

22
Data type of variable x and y<class 'int'><class 'int'>
1.2
Data type of variable d is <class 'float'>
Arvin Education
Data type of variable s is <class 'str'>

That is all for this post. In the next post we will see control statements in python.

Please see https://machinelearningtamil.blogspot.com/ for தமிழ் Version of this post.

Happy coding