Add "average" filter operator for arithmetic mean (#5612)

core/modules/filters/math.js

@@ -125,6 +125,54 @@ exports.minall = makeNumericReducingOperator(
 	Infinity // Initial value
 );
 
+exports.median = makeNumericArrayOperator(
+	function(values) {
+		var len = values.length, median;
+		values.sort();
+		if(len % 2) { 
+			// Odd, return the middle number
+			median = values[(len - 1) / 2];
+		} else {
+			// Even, return average of two middle numbers
+			median = (values[len / 2 - 1] + values[len / 2]) / 2;
+		}
+		return [median];
+	}
+);
+
+exports.average = makeNumericReducingOperator(
+	function(accumulator,value) {return accumulator + value},
+	0, // Initial value
+	function(finalValue,numberOfValues) {
+		return finalValue/numberOfValues;
+	}
+);
+
+exports.variance = makeNumericReducingOperator(
+	function(accumulator,value) {return accumulator + value},
+	0,
+	function(finalValue,numberOfValues,originalValues) {
+		return getVarianceFromArray(originalValues,finalValue/numberOfValues);
+	}
+);
+
+exports["standard-deviation"] = makeNumericReducingOperator(
+	function(accumulator,value) {return accumulator + value},
+	0,
+	function(finalValue,numberOfValues,originalValues) {
+		var variance = getVarianceFromArray(originalValues,finalValue/numberOfValues);
+		return Math.sqrt(variance);
+	}
+);
+
+//Calculate the variance of a population of numbers in an array given its mean
+function getVarianceFromArray(values,mean) {
+	var deviationTotal = values.reduce(function(accumulator,value) {
+		return accumulator + Math.pow(value - mean, 2);
+	},0);
+	return deviationTotal/values.length;
+};
+
 function makeNumericBinaryOperator(fnCalc) {
 	return function(source,operator,options) {
 		var result = [],
@@ -134,19 +182,37 @@ function makeNumericBinaryOperator(fnCalc) {
 		});
 		return result;
 	};
-}
+};
 
-function makeNumericReducingOperator(fnCalc,initialValue) {
+function makeNumericReducingOperator(fnCalc,initialValue,fnFinal) {
 	initialValue = initialValue || 0;
 	return function(source,operator,options) {
 		var result = [];
 		source(function(tiddler,title) {
-			result.push(title);
+			result.push($tw.utils.parseNumber(title));
 		});
-		return [$tw.utils.stringifyNumber(result.reduce(function(accumulator,currentValue) {
-			return fnCalc(accumulator,$tw.utils.parseNumber(currentValue));
-		},initialValue))];
+		var value = result.reduce(function(accumulator,currentValue) {
+				return fnCalc(accumulator,currentValue);
+			},initialValue);
+		if(fnFinal) {
+			value = fnFinal(value,result.length,result);
+		}
+		return [$tw.utils.stringifyNumber(value)];
 	};
-}
+};
+
+function makeNumericArrayOperator(fnCalc) {
+	return function(source,operator,options) {
+		var results = [];
+		source(function(tiddler,title) {
+			results.push($tw.utils.parseNumber(title));
+		});
+		results = fnCalc(results);
+		$tw.utils.each(results,function(value,index) {
+			results[index] = $tw.utils.stringifyNumber(value);
+		});
+		return results;
+	};
+};
 
 })();

editions/test/tiddlers/tests/test-prefixes-filter.js

@@ -298,6 +298,28 @@ describe("'reduce' and 'intersection' filter prefix tests", function() {
 		expect(wiki.filterTiddlers("[tag[non-existent]reduce<add-price>else[0]]",anchorWidget).join(",")).toBe("0");
 	});
 
+	it("should handle the average operator", function() {
+		expect(wiki.filterTiddlers("[tag[shopping]get[price]average[]]").join(",")).toBe("2.3575");
+		expect(parseFloat(wiki.filterTiddlers("[tag[food]get[price]average[]]").join(","))).toBeCloseTo(3.155);
+	});
+
+	it("should handle the median operator", function() {
+		expect(parseFloat(wiki.filterTiddlers("[tag[shopping]get[price]median[]]").join(","))).toBeCloseTo(1.99);
+		expect(parseFloat(wiki.filterTiddlers("[tag[food]get[price]median[]]").join(","))).toBeCloseTo(3.155);
+	});
+	
+	it("should handle the variance operator", function() {
+		expect(parseFloat(wiki.filterTiddlers("[tag[shopping]get[price]variance[]]").join(","))).toBeCloseTo(2.92);
+		expect(parseFloat(wiki.filterTiddlers("[tag[food]get[price]variance[]]").join(","))).toBeCloseTo(3.367);
+		expect(wiki.filterTiddlers(" +[variance[]]").toString()).toBe("NaN");
+	});
+
+	it("should handle the standard-deviation operator", function() {
+		expect(parseFloat(wiki.filterTiddlers("[tag[shopping]get[price]standard-deviation[]]").join(","))).toBeCloseTo(1.71);
+		expect(parseFloat(wiki.filterTiddlers("[tag[food]get[price]standard-deviation[]]").join(","))).toBeCloseTo(1.835);
+		expect(wiki.filterTiddlers(" +[standard-deviation[]]").toString()).toBe("NaN");
+	});	
+
 	it("should handle the :intersection prefix", function() {
 		expect(wiki.filterTiddlers("[[Sparkling water]tags[]] :intersection[[Red wine]tags[]]").join(",")).toBe("drinks,textexample");
 		expect(wiki.filterTiddlers("[[Brownies]tags[]] :intersection[[Chocolate Cake]tags[]]").join(",")).toBe("food");

editions/tw5.com/tiddlers/filters/Mathematics Operators.tid

@@ -1,5 +1,5 @@
 created: 20190206140446821
-modified: 20190611155838557
+modified: 20210417090408263
 tags: Filters
 title: Mathematics Operators
 type: text/vnd.tiddlywiki
@@ -26,6 +26,7 @@ The mathematics operators take three different forms:
 * ''Reducing operators'' apply an operation to all of the numbers in the input list, returning a single result (e.g. sum, product)
 ** <<.inline-operator-example "=1 =2 =3 =4 +[sum[]]">>
 ** <<.inline-operator-example "=1 =2 =3 =4 +[product[]]">>
+** <<.inline-operator-example "=1 =2 =3 =4 +[average[]]">>
 
 Operators can be combined:
 

editions/tw5.com/tiddlers/filters/average.tid

@@ -0,0 +1,13 @@
+caption: average
+created: 20210417090137714
+modified: 20210426131553482
+op-input: a [[selection of titles|Title Selection]]
+op-output: the arithmetic mean of the input as numbers
+op-purpose: treating each input title as a number, compute their arithmetic mean
+tags: [[Reducing Mathematics Operators]] [[Filter Operators]] [[Mathematics Operators]]
+title: average Operator
+type: text/vnd.tiddlywiki
+
+<<.from-version "5.1.24">> See [[Mathematics Operators]] for an overview.
+
+<<.operator-examples "average">>

editions/tw5.com/tiddlers/filters/examples/average Operator (Examples).tid

@@ -0,0 +1,10 @@
+created: 20210426130837644
+modified: 20210426131553546
+tags: [[Operator Examples]] [[average Operator]]
+title: average Operator (Examples)
+type: text/vnd.tiddlywiki
+
+<<.operator-example 1 "=1 =3 =4 =5 +[average[]]">>
+
+Note that if there is no input the operator returns `NaN`
+<<.operator-example 2 "[tag[NotATiddler]get[price]] +[average[]]">>

editions/tw5.com/tiddlers/filters/examples/median Operator (Examples).tid

@@ -0,0 +1,10 @@
+created: 20210426131042769
+modified: 20210426131553560
+tags: [[Operator Examples]] [[median Operator]]
+title: median Operator (Examples)
+type: text/vnd.tiddlywiki
+
+<<.operator-example 1 "=1 =3 =4 =5 +[median[]]">>
+
+Note that if there is no input the operator returns `NaN`
+<<.operator-example 2 "[title[NotATiddler]get[price]] +[median[]]">>

editions/tw5.com/tiddlers/filters/examples/standard-deviation Operator (Examples).tid

@@ -0,0 +1,10 @@
+created: 20210426130306824
+modified: 20210426131553553
+tags: [[Operator Examples]] [[standard-deviation Operator]]
+title: standard-deviation Operator (Examples)
+type: text/vnd.tiddlywiki
+
+<<.operator-example 1 "=1 =3 =4 =5 +[standard-deviation[]]">>
+
+Note that if there is no input the operator returns `NaN`
+<<.operator-example 2 "[title[NotATiddler]get[price]] +[standard-deviation[]]">>

editions/tw5.com/tiddlers/filters/examples/variance Operator (Examples).tid

@@ -0,0 +1,10 @@
+created: 20210426130620777
+modified: 20210426131553522
+tags: [[Operator Examples]] [[variance Operator]]
+title: variance Operator (Examples)
+type: text/vnd.tiddlywiki
+
+<<.operator-example 1 "1 3 4 5 +[variance[]]">>
+
+Note that if there is no input the operator returns `NaN`
+<<.operator-example 2 "[title[NotATiddler]is[tiddler]get[price]] +[variance[]]">>

editions/tw5.com/tiddlers/filters/median.tid

@@ -0,0 +1,13 @@
+caption: median
+created: 20210417090137714
+modified: 20210426131553507
+op-input: a [[selection of titles|Title Selection]]
+op-output: the median of the input numbers
+op-purpose: treating each input title as a number, compute their median value
+tags: [[Filter Operators]] [[Mathematics Operators]]
+title: median Operator
+type: text/vnd.tiddlywiki
+
+<<.from-version "5.1.24">> See [[Mathematics Operators]] for an overview.
+
+<<.operator-examples "median">>

editions/tw5.com/tiddlers/filters/standard-deviation Operator.tid

@@ -0,0 +1,15 @@
+caption: standard-deviation
+created: 20210426130150358
+modified: 20210426131553530
+op-input: a [[selection of titles|Title Selection]]
+op-output: the standard-deviation of the input as numbers
+op-purpose: treating each input title as a number, compute their standard-deviation
+tags: [[Reducing Mathematics Operators]] [[Filter Operators]] [[Mathematics Operators]]
+title: standard-deviation Operator
+type: text/vnd.tiddlywiki
+
+<<.from-version "5.1.24">> See [[Mathematics Operators]] for an overview.
+
+<<.tip """ The `standard-deviation` operator treats the input as a complete population and not a sample""">>
+
+<<.operator-examples "standard-deviation">>

editions/tw5.com/tiddlers/filters/variance Operator.tid

@@ -0,0 +1,15 @@
+caption: variance
+created: 20210426130029500
+modified: 20210426131553539
+op-input: a [[selection of titles|Title Selection]]
+op-output: the variance of the input as numbers
+op-purpose: treating each input title as a number, compute their variance
+tags: [[Reducing Mathematics Operators]] [[Filter Operators]] [[Mathematics Operators]]
+title: variance Operator
+type: text/vnd.tiddlywiki
+
+<<.from-version "5.1.24">> See [[Mathematics Operators]] for an overview.
+
+<<.tip """ The `standard-deviation` operator treats the input as a complete population and not a sample""">>
+
+<<.operator-examples "variance">>