Category Archives: Javascript

Code of the Day: Sentence Scrambler

Posted by on January 4, 2012 No comments

Task:
There was a study going out a few years ago that said people can read words that are scrambled if the first and last character are left in place. So to help me practice Test Driven Development, I decided program it.
Example:
Correct: “Create attractive offers to reach the right customers”
Scrambled: “Cterae aacrtvitte offres to recah the rghit couemtrss”

For more information about the study visit: Cambridge Word Scramble Study: It’s Fake Already!

Code:

/**
* @author: Larry Battle
* @date: January 2, 2012
* @purpose: Scrambler - to scramble the alphabetical letters in word in such a way to make it still readable and understandable.
* @note: This can be accomplished by have perversing the word order but mixing up every letter in the word except for the first.
*/
var scrambler = {
	scrambleStr : function( str ){
		if( typeof str !== 'string' ){
			return -1;
		}
		return str.replace( /[^\s]*/g, function( word ){			
			return word ? scrambler.scrambleWord( word ) : word;
		});
	},
	scrambleWord :  function( str ){
		if( typeof str !== 'string' ){
			return str;
		}
		str = str.replace( /[a-z]*/ig, function( str2 ){
			if( str2 && str2.length > 2 ){
				str2 = str2.charAt(0) + scrambler.randomizeStr( str2.substring( 1, str2.length - 1 ) ) + str2.charAt( str2.length - 1 );
			}
			return str2;
		});
		return str;
	},
	randomizeStr : function( str ){
		if( typeof str !== 'string' ){
			return str;
		}
		return scrambler.makeArrayRandom( str.split( '' ) ).join( '' );
	},
	makeArrayRandom : function( arr ){
		var j, x, i = arr.length;
		while( i ){
				j = parseInt(Math.random() * i, 10);
				x = arr[--i]; 
				arr[i] = arr[j];
				arr[j] = x;
		}
		return arr;
	}
};

Input:

var str = "I can't believe what I'm reading."
scrambler.scrambleStr( str );

Output: (Possible outcome)

"I can't beilvee waht I'm rndiaeg."

Try it out for yourself.
Demo: Scrambler

Improved Code for Javascript Decimal to Fraction

Posted by on November 26, 2011 No comments

This post improves the code at “Code of the Day Javascript Decimal to fraction” by using Euclid’s Algorithm to find the Great Common Factor or GCF, aka GCD. This method provides a speed up of 10x when compared to the original algorithm posted.

Code

/**
*@function gcd (aka Euclid's algorithm)
*@purpose returns the greatest common factor between two numbers;
*/
function gcd(a, b) {
    return (b) ? gcd(b, a % b) : a;
}
/**
*@function dec2Frac
*@purpose returns a decimal as a fraction.
*/
var dec2Frac = function ( num ) {
	var top = num.toString().replace(/\d+[.]/, '');
	var bot = Math.pow(10, top.length);
	if (num > 1) {
		top = +top + Math.floor(num) * bot;
	}
	var x = gcd(top, bot);
	return (top / x) + "/" + (bot / x);
};

Usage

dec2Frac( 1.24325 ) // returns "4973/4000"
dec2Frac( 2.45 ) // returns "49/20"

Speed Test between Version 1 and 2 of dec2Frac()

//@requires Firebug or Chrome Developer Tools
//The following code test the speed difference between the Version 1 and 2 of dec2Frac.
function gcd(a, b) {
    return (b) ? gcd(b, a % b) : a;
}
var dec2FracV2 = function (d) {
	var top = d.toString().replace(/\d+[.]/, '');
	var bot = Math.pow(10, top.length);
	if (d > 1) {
		top = +top + Math.floor(d) * bot;
	}
	var x = gcd(top, bot);
	return (top / x) + "/" + (bot / x);
};
function dec2FracV1(d) {
    var df = 1, top = 1, bot = 1;
    var limit = 1e5; //Increase the limit to get more precision.
 
    while (df != d && limit-- > 0) {
        if (df < d) {
            top += 1;
        }
        else {
            bot += 1;
            top = parseInt(d * bot, 10);
        }
        df = top / bot;
    }
    return top + '/' + bot;
}
var getRandomNum = function (i, decLen) {
	return (Math.random() * (i || 1)).toFixed(decLen);
};
 
var runTest = function ( funcName ) {
	var func = { "V1": dec2FracV1, "V2": dec2FracV2 }[ funcName ];
	var i = 1000;
	while (i--) {
		num = getRandomNum(10, 4);
		var x = func(num);
		if (num != eval(x)) {
			console.warn("ERROR: Function %s, The fraction %s != %s", funcName, num, x);
		}
	}
};
console.time( 'V1' );
runTest( "V1" );
console.timeEnd( 'V1' );
 
console.time( 'V2' );
runTest( "V2" );
console.timeEnd( 'V2' );

Chrome Result:
V1: 11628ms
V2: 185ms

Try the test out yourself
jsbin.com

Code of the Day: Javascript Decimal To Fraction

Posted by on November 26, 2011 1 comment

Source: mivk from StackOverflow.com
Code

/**
@function dec2frac
@returns string
@purpose Convert a decimal to a fraction
*/
function dec2frac(d) {
    var df = 1, top = 1, bot = 1;
    var limit = 1e5; //Increase the limit to get more precision.
 
    while (df != d && limit-- > 0) {
        if (df < d) {
            top += 1;
        }
        else {
            bot += 1;
            top = parseInt(d * bot, 10);
        }
        df = top / bot;
    }
    return top + '/' + bot;
}

Demo
JSBIN link

Example Output
dec2frac ( 0.1) returns “1/10″
dec2frac ( 0.2) returns “1/5″
dec2frac ( 0.5) returns “1/2″
dec2frac ( 0.9999) returns “9999/10000″
dec2frac ( 0.75) returns “3/4″
dec2frac ( 2.718281828459045) returns “135915/50000″, but this evaluates to 2.7183
dec2frac ( 3.141592653589793) returns “157079/50000″, but this evaluates to 3.14158

Code of the day: Javascript convert bytes to KB, MB, GB, etc

Posted by on August 24, 2011 No comments 
/**
* @function: getBytesWithUnit()
* @purpose: Converts bytes to the most simplified unit.
* @param: (number) bytes, the amount of bytes
* @returns: (string)
*/
var getBytesWithUnit = function( bytes ){
	if( isNaN( bytes ) ){ return; }
	var units = [ ' bytes', ' KB', ' MB', ' GB', ' TB', ' PB', ' EB', ' ZB', ' YB' ];
	var amountOf2s = Math.floor( Math.log( +bytes )/Math.log(2) );
	if( amountOf2s < 1 ){
		amountOf2s = 0;
	}
	var i = Math.floor( amountOf2s / 10 );
	bytes = +bytes / Math.pow( 2, 10*i );
 
	// Rounds to 3 decimals places.
        if( bytes.toString().length > bytes.toFixed(3).toString().length ){
            bytes = bytes.toFixed(3);
        }
	return bytes + units[i];
};

Output:

console.log( getBytesWithUnit( ) );			// returns undefined.
console.log( getBytesWithUnit( 'non a number.' ) );	// returns undefined.
console.log( getBytesWithUnit( '123' ));		// returns '123 bytes'.
console.log( getBytesWithUnit( 1024 ));		// returns '1 KB'.
console.log( getBytesWithUnit( (1024 * 1024) + 1024 )); // returns '1.001 MB'.
console.log( getBytesWithUnit( 1024 * 1024 * 1024 )); // returns '1 GB'.
console.log( getBytesWithUnit( 1024 * 1024 * 64 )); // returns '64 MB'.

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