Cleaner comments, all reduction functions return add, rem, ini, acc, …

…for brevity

crossfilter-helpers.js

@@ -1,129 +1,183 @@
 var exports = (function(e){
 	'use strict';
 
-	// reduce by the number of elements of a group
+	/**
+	 reduce by the number of elements of a group
+	 initial value: 0
+	*/
 	e.count = function(){
 		return {
 			add : function(p, v){
 				p.count++;
 				return p;
 			},
-			remove : function(p, v){
+			rem : function(p, v){
 				p.count--;
 				return p;
 			},
-			init : function(){
-				return { count : 0 };
+			ini : function(){
+				return {
+					count : 0
+				};
 			},
-			access : function(p){
+			acc : function(p){
 				return p.count;
 			}
 		}
 	};
 
-	// reduce by the sum of elements of a group
+	/**
+	 reduce by the sum of elements of a group
+	 initial value: 0
+	*/
 	e.sum = function(fn){
 		return {
 			add : function(p, v){
 				p.sum += fn(v);
 				return p;
 			},
-			remove : function(p, v){
+			rem : function(p, v){
 				p.sum -= fn(v);
 				return p;
 			},
-			init : function(){
-				return { sum : 0 };
+			ini : function(){
+				return {
+					sum : 0
+				};
 			},
-			access : function(p){
+			acc : function(p){
 				return p.sum;
 			}
 		}
 	};
 
-	// reduce by the product of elements of a group, initially set to 1
+	/**
+	 reduce by the product of elements of a group
+	 initial value: 1
+	*/
 	e.product = function(fn){
 		return {
 			add : function(p, v){
 				p.product *= fn(v);
 				return p;
 			},
-			remove : function(p, v){
-				p.product /= fn(v);
+			rem : function(p, v){
+				p.product = fn(v) != 0 ? p.product / fn(v) : p.product;
 				return p;
 			},
-			init : function(){
-				return { product : 1 };
+			ini : function(){
+				return {
+					product : 1
+				};
 			},
-			access : function(p){
+			acc : function(p){
 				return p.product;
 			}
 		}
 	};
 
-	// reduce by maximum value, initially set to -Infinity
+	/**
+	 reduce by maximum value among elements of a group
+	 initial value: -Infinity
+	*/
 	e.max = function(fn){
 		return {
 			add : function(p, v){
 				p.max = fn(v) > p.max ? fn(v) : p.max;
 				return p;
 			},
-			remove : function(p, v){
+			rem : function(p, v){
 				p.max = fn(v) > p.max ? fn(v) : p.max;
 				return p;
 			},
-			init : function(){
-				return { max : -Infinity };
+			ini : function(){
+				return {
+					max : -Infinity
+				};
 			},
-			access : function(p){
+			acc : function(p){
 				return p.max;
 			}
 		}
 	};
 
-	// reduce by minimum value, initially set to +Infinity
+	/**
+	 reduce by minimum value among elements of a group
+	 initial value: Infinity
+	*/
 	e.min = function(fn){
 		return {
 			add : function(p, v){
 				p.min = fn(v) < p.min ? fn(v) : p.min;
 				return p;
 			},
-			remove : function(p, v){
+			rem : function(p, v){
 				p.min = fn(v) < p.min ? fn(v) : p.min;
 				return p;
 			},
-			init : function(){
-				return { min : Infinity };
+			ini : function(){
+				return {
+					min : Infinity
+				};
 			},
-			access : function(p){
+			acc : function(p){
 				return p.min;
 			}
 		}
 	};
 
-	// reduce by the (weighted) mean of elements of a group
-	// if weight is not set, constant 1 is assumed
-	// if weight equals 0, sum is not changed (current record is ignored)
-	// if count equals 0, mean is zeroed
+	// reduce by spread, meaning the difference between the mininum and the maximum of the group
+	// e.spread = function(fn){
+	// 	return {
+	// 		add : function(p, v){
+	// 			p.min = fn(v) < p.min ? fn(v) : p.min;
+	// 			return p;
+	// 		},
+	// 		rem : function(p, v){
+	// 			p.min = fn(v) < p.min ? fn(v) : p.min;
+	// 			return p;
+	// 		},
+	// 		ini : function(){
+	// 			return {
+	// 				spread : 0,
+	// 				min    : Infinity,
+	// 				max    : -Infinity
+	// 			};
+	// 		},
+	// 		acc : function(p){
+	// 			return p.spread;
+	// 		}
+	// 	}
+	// };
+
+	/**
+	 reduce by the (weighted) mean of elements of a group
+	 if weight is not set, constant 1 is assumed
+	 initial value: 0
+	*/
 	e.mean = function(fn_f, fn_w){
-		var w = typeof fn_w === 'function' ? fn_w : e.helper_constant(1);
+		var w = typeof fn_w === 'undefined' ? e.helper_constant(1) : fn_w;
 		return {
 			add : function(p, v){
-				p.count += w(v);
 				p.sum   += fn_f(v) * w(v);
+				p.count += w(v);
 				p.mean   = p.count ? p.sum / p.count : 0;
 				return p;
 			},
-			remove : function(p, v){
-				p.count -= w(v);
+			rem : function(p, v){
 				p.sum   -= fn_f(v) * w(v);
+				p.count -= w(v);
 				p.mean   = p.count ? p.sum / p.count : 0;
 				return p;
 			},
-			init : function(){
-				return { count : 0, sum : 0, mean : 0 };
+			ini : function(){
+				return {
+					count : 0,
+					sum   : 0,
+					mean  : 0
+				};
 			},
-			access : function(p){
+			acc : function(p){
 				return p.mean;
 			}
 		}
@@ -137,6 +191,19 @@ module.exports = exports;
 var exports = (function(e){
 	'use strict';
 
+	// build a general data accessor for reduce() parameter functions
+	// if f is a function, it will return this function
+	// otherwise it will build a function that, given a datum d,
+	// will return d[f]
+	e.helper_accessor = function(f) {
+		if (typeof f != 'function') {
+			return function(d) {
+				return d[f];
+			}
+		}
+		return f;
+	}
+
 	// build a function returning a selected variable
 	e.helper_constant = function(c) {
 		return function() {