Merge pull request #326 from Skeeve/listops

New list operations from @Skeeve

core/modules/filters/listops.js

@@ -0,0 +1,116 @@
+/*\
+title: $:/core/modules/filters/listops.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operator for manipulating lists
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Export our filter function
+*/
+exports.reverse = function(source,operator,options) {
+	var results = [];
+	// Iterate through the source tiddlers
+	if($tw.utils.isArray(source)) {
+		$tw.utils.each(source,function(title) {
+			results.unshift(title);
+		});
+	} else {
+		$tw.utils.each(source,function(element,title) {
+			results.unshift(title);
+		});
+	}
+	return results;
+};
+
+exports.first = function(source,operator,options) {
+	var results = [];
+	var count = operator.operand || 1;
+	// Iterate through the source tiddlers
+	if($tw.utils.isArray(source)) {
+		results = source.slice(0, Math.min(count, source.length));
+	} else {
+		for(var title in source) {
+			if(count-- < 1) break;
+			results.push(title);
+		};
+	}
+	return results;
+};
+
+exports.last = function(source,operator,options) {
+	var results = [];
+	var count = operator.operand || 1;
+	// Iterate through the source tiddlers
+	if($tw.utils.isArray(source)) {
+		results = source.slice(-count);
+	} else {
+		for(var title in source) {
+			results.push(title);
+		};
+		results = results.slice(-count);
+	}
+	return results;
+};
+
+exports.rest = function(source,operator,options) {
+	var results = [];
+	var count = operator.operand || 1;
+	// Iterate through the source tiddlers
+	if($tw.utils.isArray(source)) {
+		results = source.slice(count);
+	} else {
+		for(var title in source) {
+			if(--count < 0) {
+				results.push(title);
+			}
+		};
+	}
+	return results;
+};
+
+exports.butfirst = exports.rest;
+exports.bf = exports.rest;
+
+exports.butlast = function(source,operator,options) {
+	var results = [];
+	var count = operator.operand || 1;
+	// Iterate through the source tiddlers
+	if($tw.utils.isArray(source)) {
+		results = source.slice(0,-count);
+	} else {
+		for(var title in source) {
+			results.push(title);
+		};
+		results = results.slice(0,-count);
+	}
+	return results;
+};
+exports.bl = exports.butlast;
+
+exports.nth = function(source,operator,options) {
+	var results = [];
+	var count = operator.operand || 1;
+	// Iterate through the source tiddlers
+	if($tw.utils.isArray(source)) {
+		results = source.slice(count-1,count);
+	} else {
+		for(var title in source) {
+			--count;
+			if(count > 0) continue;
+			if(count < 0) break;
+			results.push(title);
+			break;
+		};
+	}
+	return results;
+};
+
+})();

editions/tw5.com/tiddlers/concepts/TiddlerFilters.tid

@@ -59,6 +59,16 @@ A filter string consists of one or more runs of filter operators that each look
 * ''sameday'': selects all the tiddlers falling into the same day as the provided date in the specified date field
 * ''fields'': returns the names of the fields present on the selected tiddlers
 * ''search'': returns all tiddlers that contain the specified text
+* ''reverse'': reverses the list
+* ''first'': selects the first tiddler of the list (or the first n if the operand is n)
+* ''last'': selects the last tiddler of the list (or the last n if the operand is n)
+* ''rest'': selects all but the first tiddler of the list (or all but the first n if the operand is n)
+* ''butfirst'': synonym for ''rest''
+* ''bf'': another synonym for ''rest''
+* ''butlast'': selects all but the last tiddler of the list (or all but the last n if the operand is n)
+* ''bl'': another synonym for ''butlast''
+* ''nth'': selects the n-th tiddler of the list. Defaults to n = 1.
+
 
 An operator can be negated with by preceding it with `!`, for example `[!tag[Tommy]]` selects the tiddlers that are not tagged with `Tommy`.