Skip to content

Instantly share code, notes, and snippets.

@goulu
Last active Sep 30, 2015
Embed
What would you like to do?
/*
Google Spreadsheet custom functions for Benford Law statistics
author : Philippe Guglielmetti aka Dr. Goulu
contact: drgoulu@gmailcom
license: LGPL
*/
function sum(a, b) { return a + b; } // not predefined ?
function log10 (arg) { return Math.log(arg) / 2.302585092994046;} // Math.LN10
function Benford(range, digit,n) {
// returns the fraction of cells in range that have their n-th digit equal to digit
// see http://en.wikipedia.org/wiki/Benford's_law
digit=String(digit);
n = typeof n !== 'undefined' ? n-1 : 0;
var process = function(cell) { return String(cell)[n]==digit ? 1:0;}
var values = range.map(process);
return values.reduce(sum, 0)/range.length;
}
function BenfordLaw(i,n){
//return probability of n-th digit to be a i according to Benford law
n = typeof n !== 'undefined' ? n : 1;
var s = 0;
if (n>1 | i>0) {
for (k=Math.floor(Math.pow(10,n-2)); k<Math.pow(10,n-1); k++) {
s+=log10(1+1/(10*k+i))
}
}
return s;
}
function Chi2(data,model){
result=0;
for (i in data) {
result=result+Math.pow(data[i]-model[i],2)/model[i];
}
return result;
}
function Chi2Benford(data,n) {
n = typeof n !== 'undefined' ? n : 1;
var s=data.reduce(sum, 0);
var b=new Array();
var d=new Array();
for (i=1; i<10; i++) {
b[i]=BenfordLaw(i,n);
d[i]=Benford(data,i,n);
}
return Chi2(d,b);
}
function main() {
Chi2Benford([3,2,1],1);
}
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment