binarymax · May 22, 2011 17:27 · ahsanvbase · Oct 16, 2014
diff --git a/annotated.js b/annotated.js
 /*******************************************
 * Powerset calculation from array 'o'.
 *
 * The cardinality of a set's Powerset is 2^n, 
 * where n is the cardinality of the set.
 *
 * This conveniently translates into an algorithm 
 * whereby all the binary representation of (0...2^n) 
 * are representitive of all possible combinations of 
 * the set, with 0.toString(2) as the empty set, and 
 * ((2^n)-1).toString() as the full set.
 *
 * For example, with set ['A','B','C']:
 *	0 == 000 == [null]
 *	1 == 001 == ['C']
 *	2 == 010 == ['B']
 *	3 == 011 == ['B','C']
 *	4 == 100 == ['A']
 *	5 == 101 == ['A','C']
 *	6 == 110 == ['A','B']
 *	7 == 111 == ['A','B','C']
 *
 *******************************************/
 function P(
 	o, //array passed in as only parameter.
 	w, //binary representation of iterator 0...(2^n)-1 (see 's' below)
 	e, //represents an iterator that loops through each bit in w 
 	r, //the powerset array that will be returned, an array of subset arrays
 	s, //iterator that steps -1 as ((2^n)-1)...0
 	E, //the length of the original set
 	t  //accounts for lack of preceding 0's in w.  For example (1).toString(2) == "1", not "001"
 ) {

 	for(r=[s=1<<(E=o.length)];s;) 	//initialize r=[(2^n)].

 		for(w=s.toString(2), 		//Store binary representaion
 			e=t=w.length,		//Length of the binary (see parameter t)
 			r[--s]=[];		//new subset
 		e;)				//e iterates over (t-1)...0

 			~-w[--e]||		//if bit in position e is 1
 			r[s].push(o[e+E-t]);	// ... add respective set item to subset
 						// ... NOTE: the subset order is reversed

 	return r				//return the powerset
 }
diff --git a/example.html b/example.html
 <!doctype html>
 <html>
  <head>
    <title>Powerset</title>
    <meta charset="utf-8" />

 	<script src="index.js" type="text/javascript"></script>

 	<script language="javascript" type="text/javascript">
 		function page_load() {

 			/*Powerset:*/
 			var Set = [1,2,3,4,5,6];
 			var Powerset = P(Set);
 			document.body.innerHTML+=JSON.stringify(Powerset);
 			document.body.innerHTML+='<br />';
 			document.body.innerHTML+=Powerset.length;

 		}
 	</script>
  </head>
  <body onload="page_load();">
  </body>
 </html>
diff --git a/index.js b/index.js
 function P(o,w,e,r,s,E,t){for(r=[s=1<<(E=o.length)];s;)for(w=s.toString(2),e=t=w.length,r[--s]=[];e;)~-w[--e]||r[s].push(o[e+E-t]);return r}
diff --git a/LICENSE.txt b/LICENSE.txt
 Copyright (c) 2011 Max Lovenheim Irwin, http://binarymax.com
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the
 "Software"), to deal in the Software without restriction, including
 without limitation the rights to use, copy, modify, merge, publish,
 distribute, sublicense, and/or sell copies of the Software, and to
 permit persons to whom the Software is furnished to do so, subject to
 the following conditions:
 
 The above copyright notice and this permission notice shall be
 included in all copies or substantial portions of the Software.
 
 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
diff --git a/package.json b/package.json
 {
  "name": "Powerset",
  "description": "P(a) returns the powerset for array a.",
  "keywords": [
    "Powerset",
    "set",
    "P"
  ]
 }
	/*******************************************
	* Powerset calculation from array 'o'.
	*
	* The cardinality of a set's Powerset is 2^n,
	* where n is the cardinality of the set.
	*
	* This conveniently translates into an algorithm
	* whereby all the binary representation of (0...2^n)
	* are representitive of all possible combinations of
	* the set, with 0.toString(2) as the empty set, and
	* ((2^n)-1).toString() as the full set.
	*
	* For example, with set ['A','B','C']:
	* 0 == 000 == [null]
	* 1 == 001 == ['C']
	* 2 == 010 == ['B']
	* 3 == 011 == ['B','C']
	* 4 == 100 == ['A']
	* 5 == 101 == ['A','C']
	* 6 == 110 == ['A','B']
	* 7 == 111 == ['A','B','C']
	*
	*******************************************/
	function P(
	o, //array passed in as only parameter.
	w, //binary representation of iterator 0...(2^n)-1 (see 's' below)
	e, //represents an iterator that loops through each bit in w
	r, //the powerset array that will be returned, an array of subset arrays
	s, //iterator that steps -1 as ((2^n)-1)...0
	E, //the length of the original set
	t //accounts for lack of preceding 0's in w. For example (1).toString(2) == "1", not "001"
	) {

	for(r=[s=1<<(E=o.length)];s;) //initialize r=[(2^n)].

	for(w=s.toString(2), //Store binary representaion
	e=t=w.length, //Length of the binary (see parameter t)
	r[--s]=[]; //new subset
	e;) //e iterates over (t-1)...0

	~-w[--e]\|\| //if bit in position e is 1
	r[s].push(o[e+E-t]); // ... add respective set item to subset
	// ... NOTE: the subset order is reversed

	return r //return the powerset
	}
	<!doctype html>
	<html>
	<head>
	<title>Powerset</title>
	<meta charset="utf-8" />

	<script src="index.js" type="text/javascript"></script>

	<script language="javascript" type="text/javascript">
	function page_load() {

	/Powerset:/
	var Set = [1,2,3,4,5,6];
	var Powerset = P(Set);
	document.body.innerHTML+=JSON.stringify(Powerset);
	document.body.innerHTML+='<br />';
	document.body.innerHTML+=Powerset.length;

	}
	</script>
	</head>
	<body onload="page_load();">
	</body>
	</html>
	Copyright (c) 2011 Max Lovenheim Irwin, http://binarymax.com

	Permission is hereby granted, free of charge, to any person obtaining
	a copy of this software and associated documentation files (the
	"Software"), to deal in the Software without restriction, including
	without limitation the rights to use, copy, modify, merge, publish,
	distribute, sublicense, and/or sell copies of the Software, and to
	permit persons to whom the Software is furnished to do so, subject to
	the following conditions:

	The above copyright notice and this permission notice shall be
	included in all copies or substantial portions of the Software.

	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
	EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
	MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
	NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
	LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
	OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
	WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
	{
	"name": "Powerset",
	"description": "P(a) returns the powerset for array a.",
	"keywords": [
	"Powerset",
	"set",
	"P"
	]
	}