Friday, December 6, 2019

Convert list comprehension to for loop in python

Lets see the concept of going from 'list comprehension' to 'for loop'.




Above is a nested python list of list that contains names of countries. The list comprehension returns the names of countries with less than ten characters.

Lets try to 'incomprehension' the list :)... more like trying to decompress it into for loop!

The "ten_character" list will start as an empty list then we append the filtered result to it from the for loops.

So, the arrangement is to take the first for loop, follow by the second for loop, then the if conditional statement and then append the result at the end. See the script below...







The complete source code:-

# List of countries...
countries = [['San Marino', 'Sao Tome and Principe', 'Saudi Arabia', 'Senegal', 'Serbia', 'Seychelles', 'Sierra Leone', 'Singapore', 'Slovakia', 'Slovenia', 'Solomon Islands', 'Somalia', 'South Africa', 'South Georgia and the South Sandwich Islands'], 
             ['Nepal', 'Netherlands', 'Netherlands Antilles', 'New Caledonia', 'New Zealand', 'Nicaragua', 'Niger', 'Nigeria', 'Niue', 'Norfolk Island', 'North Korea', 'Northern Mariana Islands', 'Norway'], 
             ['Togo', 'Tokelau', 'Tonga', 'Trinidad and Tobago', 'Tunisia', 'Turkey', 'Turkmenistan', 'Turks and Caicos Islands', 'Tuvalu', 'U.S. Minor Outlying Islands', 'U.S. Virgin Islands', 'Uganda', 'Ukraine', 'United Arab Emirates', 'United Kingdom', 'United States', 'Uruguay', 'Uzbekistan', 'Vanuatu', 'Vatican City', 'Venezuela', 'Vietnam', 'Wallis and Futuna', 'Western Sahara'], 
             ['Afghanistan', 'Albania', 'Algeria', 'American Samoa', 'Andorra', 'Angola', 'Anguilla', 'Antarctica', 'Antigua and Barbuda', 'Argentina', 'Armenia', 'Aruba', 'Australia', 'Austria', 'Azerbaijan', 'Bahamas', 'Bahrain', 'Bangladesh', 'Barbados', 'Belarus', 'Belgium', 'Belize', 'Benin', 'Bermuda', 'Bhutan', 'Bolivia', 'Bosnia and Herzegovina', 'Botswana', 'Bouvet Island', 'Brazil', 'British Indian Ocean Territory']]

# Country name less than 10 character lenght...
ten_character = [ten for sublist in countries for ten in sublist if len(ten) < 10]

print(ten_character)


# List of countries...
countries = [['San Marino', 'Sao Tome and Principe', 'Saudi Arabia', 'Senegal', 'Serbia', 'Seychelles', 'Sierra Leone', 'Singapore', 'Slovakia', 'Slovenia', 'Solomon Islands', 'Somalia', 'South Africa', 'South Georgia and the South Sandwich Islands'], 
             ['Nepal', 'Netherlands', 'Netherlands Antilles', 'New Caledonia', 'New Zealand', 'Nicaragua', 'Niger', 'Nigeria', 'Niue', 'Norfolk Island', 'North Korea', 'Northern Mariana Islands', 'Norway'], 
             ['Togo', 'Tokelau', 'Tonga', 'Trinidad and Tobago', 'Tunisia', 'Turkey', 'Turkmenistan', 'Turks and Caicos Islands', 'Tuvalu', 'U.S. Minor Outlying Islands', 'U.S. Virgin Islands', 'Uganda', 'Ukraine', 'United Arab Emirates', 'United Kingdom', 'United States', 'Uruguay', 'Uzbekistan', 'Vanuatu', 'Vatican City', 'Venezuela', 'Vietnam', 'Wallis and Futuna', 'Western Sahara'], 
             ['Afghanistan', 'Albania', 'Algeria', 'American Samoa', 'Andorra', 'Angola', 'Anguilla', 'Antarctica', 'Antigua and Barbuda', 'Argentina', 'Armenia', 'Aruba', 'Australia', 'Austria', 'Azerbaijan', 'Bahamas', 'Bahrain', 'Bangladesh', 'Barbados', 'Belarus', 'Belgium', 'Belize', 'Benin', 'Bermuda', 'Bhutan', 'Bolivia', 'Bosnia and Herzegovina', 'Botswana', 'Bouvet Island', 'Brazil', 'British Indian Ocean Territory']]



ten_character = []

for sublist in countries:
    for ten in sublist:
        if len(ten) < 10:
            ten_character.append(ten)

            
print(ten_character)





That is it!

Monday, December 2, 2019

JavaScript Recursive Factorial Algorithm

This blog post is about "Recursive Function in JavaScript". The ability for a function to call it self is know as 'Recursion'.

A recursive function has two parts namely: the base case (which gets called when the recursion is satisfied needs to terminate) and the recursive case (which continue to call the function they are in until the base case condition is satisfied)

Recursion is particularly useful for divide and conquer problems. A simple problem that naturally best solved by recursive solution is 'calculating factorials'.

The recursive factorial algorithm defines two cases:
~ the base case when x is zero, and
~ the recursive case when x is greater than zero.

Factorial of a number 'x' is the product of all positive integers less than or equal to the number 'x'. For example the factorial of 6 is: 1 x 2 x 3 x 4 x 5 x 6 = 720



The implementation is as follow:-


function myRecur_factorial(x){
    
    if (x == 1){
        return x; // This is the: Base Case
    } else{
        return(x * myRecur_factorial(x-1)) // This is the: Recursive Case
    }
}

x = 6

console.log(`The factorial of ${x} is: ` + myRecur_factorial(x))


Recursion and Iteration are somewhat similar and often confused by programmers because they both repeat a series of operations. It is mostly not clear if recursion or iteration is a better solution to a particular problem. The following table highlights some differences between recursion and iteration:

Recursion
Iteration
When the base case is reached, it terminates
It terminates when a defined condition is met
Space in memory is required to store each  recursive call
Iteration is not stored in memory
Stack Overflow Error occurs when a recursion is  infinite
Infinite iteration will not return error












Another example of recursion is when we used a recursive approach to generating all the possible permutations of a given string, X, of a given length Y: