ShannonEntropy ( text )

A function for calculating the entropy of a string - how difficult is it to encode.

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Richard Dyce - Show more from this author
Dyce & Sons Ltd.
http://dyce.com

Sample input:

ShannonEntropy ( "aaaaaa" )

ShannonEntropy ( "aaaabb" )

ShannonEntropy ( "abcdefg" )

ShannonEntropy ( "This is some text. It is very long" )

Sample output:

0

.9182958340544895

2.8073549220576048

3.7958114600475881

Function definition: (Copy & paste into FileMaker's Edit Custom Function window)

// ShannonEntropy ( text )
// Used for calculating the strength of passwords

Let(
	[
		values = LetterCount ( text ; "" ) ;
		n = Length ( text ) ;

		get_frequency = "GetAsNumber ( Middle( [t] ; 2 ; 10 ) ) / " & n  ;
		frequencies = ApplyToList ( get_frequency ; values ; ¶ ) ;
		
		get_entropy = "[n] * Lg( [n] )"  ;
		entropies = Substitute( ApplyToList ( get_entropy ; frequencies ; ¶ ) ; [  ¶ ; " + " ] ; [  "-" ; "0" ] )
	];
	Evaluate( Substitute( entropies ; ¶ ; " + " ) )
)

The Shannon Entropy is the minimal number of bits per symbol needed to encode the information in binary form. It's a good rule of thumb measure of how strong your password is ;-)

Comments

		Peter Gerlings, Amsterdam Jan 1, 2018
This seems to reference two custom functions. I can find one by the same author on this site, but I canâ€™t find one for â€œApplyToListâ€. If the author sees this, please provide references to the appropriate subroutines. This would be very useful for me, but I canâ€™t get it to work. Thanks!

		Richard Dyce, Dyce & Sons Ltd. Jan 1, 2018
The ApplyToList() function is the standard function by Debi Fuchs: http://www.briandunning.com/cf/899

		Peter Gerlings, Amsterdam Jan 7, 2018
Thanks!

Note: these functions are not guaranteed or supported by BrianDunning.com. Please contact the individual developer with any questions or problems.

ShannonEntropy ( text )

Comments

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