Add a function to filter items out of the legend

docs/01-Chart-Configuration.md

@@ -154,6 +154,7 @@ fontColor | Color | "#666" | Font color inherited from global configuration
 fontFamily | String | "'Helvetica Neue', 'Helvetica', 'Arial', sans-serif" | Font family inherited from global configuration
 padding | Number | 10 | Padding between rows of colored boxes
 generateLabels: | Function | `function(chart) {  }` | Generates legend items for each thing in the legend. Default implementation returns the text + styling for the color box. See [Legend Item](#chart-configuration-legend-item-interface) for details.
+filter | Function | null | Filters legend items out of the legend. Receives 2 parameters, a [Legend Item](#chart-configuration-legend-item-interface) and the chart data
 usePointStyle | Boolean | false | Label style will match corresponding point style (size is based on fontSize, boxWidth is not used in this case).
 
 #### Legend Item Interface

src/core/core.legend.js

@@ -162,10 +162,20 @@ module.exports = function(Chart) {
 		beforeBuildLabels: noop,
 		buildLabels: function() {
 			var me = this;
-			me.legendItems = me.options.labels.generateLabels.call(me, me.chart);
-			if (me.options.reverse) {
-				me.legendItems.reverse();
+			var labelOpts = me.options.labels;
+			var legendItems = labelOpts.generateLabels.call(me, me.chart);
+
+			if (labelOpts.filter) {
+				legendItems = legendItems.filter(function(item) {
+					return labelOpts.filter(item, me.chart.data);
+				});
 			}
+
+			if (me.options.reverse) {
+				legendItems.reverse();
+			}
+
+			me.legendItems = legendItems;
 		},
 		afterBuildLabels: noop,
 

test/core.legend.tests.js

@@ -90,6 +90,71 @@ describe('Legend block tests', function() {
 		}]);
 	});
 
+	it('should filter items', function() {
+		var chart = window.acquireChart({
+			type: 'bar',
+			data: {
+				datasets: [{
+					label: 'dataset1',
+					backgroundColor: '#f31',
+					borderCapStyle: 'butt',
+					borderDash: [2, 2],
+					borderDashOffset: 5.5,
+					data: []
+				}, {
+					label: 'dataset2',
+					hidden: true,
+					borderJoinStyle: 'miter',
+					data: [],
+					legendHidden: true
+				}, {
+					label: 'dataset3',
+					borderWidth: 10,
+					borderColor: 'green',
+					pointStyle: 'crossRot',
+					data: []
+				}],
+				labels: []
+			},
+			options: {
+				legend: {
+					labels: {
+						filter: function(legendItem, data) {
+							var dataset = data.datasets[legendItem.datasetIndex];
+							return !dataset.legendHidden;
+						}
+					}
+				}
+			}
+		});
+
+		expect(chart.legend.legendItems).toEqual([{
+			text: 'dataset1',
+			fillStyle: '#f31',
+			hidden: false,
+			lineCap: 'butt',
+			lineDash: [2, 2],
+			lineDashOffset: 5.5,
+			lineJoin: undefined,
+			lineWidth: undefined,
+			strokeStyle: undefined,
+			pointStyle: undefined,
+			datasetIndex: 0
+		}, {
+			text: 'dataset3',
+			fillStyle: undefined,
+			hidden: false,
+			lineCap: undefined,
+			lineDash: undefined,
+			lineDashOffset: undefined,
+			lineJoin: undefined,
+			lineWidth: 10,
+			strokeStyle: 'green',
+			pointStyle: 'crossRot',
+			datasetIndex: 2
+		}]);
+	});
+
 	it('should draw correctly', function() {
 		var chart = window.acquireChart({
 			type: 'bar',