From ca51634041d0c7dd358f04b06d760bb5b0418def Mon Sep 17 00:00:00 2001
From: Jeremy Ruston <jeremy@osmosoft.com>
Date: Mon, 27 May 2013 17:59:03 +0100
Subject: [PATCH] Add the `each` filter operator

This makes it possible to do grouping within lists
---
 core/modules/filters/each.js | 42 ++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 core/modules/filters/each.js

diff --git a/core/modules/filters/each.js b/core/modules/filters/each.js
new file mode 100644
index 000000000..aad58cea1
--- /dev/null
+++ b/core/modules/filters/each.js
@@ -0,0 +1,42 @@
+/*\
+title: $:/core/modules/filters/each.js
+type: application/javascript
+module-type: filteroperator
+
+Filter operator that selects one tiddler for each unique value of the specified field
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+/*
+Export our filter function
+*/
+exports.each = function(source,operator,options) {
+	// Convert the source to an array if necessary
+	if(!$tw.utils.isArray(source)) {
+		var copy = [];
+		$tw.utils.each(source,function(element,title) {
+			copy.push(title);
+		});
+		source = copy;
+	}
+	// Collect up the first tiddler with each unique value of the specified field
+	var results = [],values = {};
+	$tw.utils.each(source,function(title) {
+		var tiddler = options.wiki.getTiddler(title);
+		if(tiddler) {
+			var value = tiddler.getFieldString(operator.operand);
+			if(!$tw.utils.hop(values,value)) {
+				values[value] = true;
+				results.push(title);
+			}
+		}
+	});
+	return results;
+};
+
+})();