Adding support for y-axis count following d3 algorithm

spec/axis-spec.js

@@ -65,6 +65,36 @@ describe('c3 chart axis', function () {
 
     });
 
+
+    describe('axis.y.tick.exact', function () {
+
+        it('should update args to have 12 ticks on y axis', function () {
+            args.axis.y.tick.count = 12;
+            expect(true).toBeTruthy();
+        });
+
+        it('should display exact count numbers', function () {
+           var text = d3.select('.c3-axis-y').selectAll('g.tick').filter(function (d, i) { 
+               return i === 1;
+           }).select('text').text();
+
+           expect(+text).toBe(13.545454545454547);
+       });
+
+        it('should update args to not to be exact ticks on y axis', function () {
+           args.axis.y.tick.exact = false;
+           expect(true).toBeTruthy();
+       });
+
+        it('should display average count numbers', function () {
+           var text = d3.select('.c3-axis-y').selectAll('g.tick').filter(function (d, i) { 
+               return i === 1;
+           }).select('text').text();
+
+           expect(+text).toBe(50);
+       });
+    });
+
     describe('axis.y.tick.values', function () {
 
         var values = [100, 500];

src/axis.js

@@ -76,12 +76,13 @@ Axis.prototype.updateXAxisTickValues = function updateXAxisTickValues(targets, a
     }
     return tickValues;
 };
-Axis.prototype.getYAxis = function getYAxis(scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition, withoutRotateTickText) {
+Axis.prototype.getYAxis = function getYAxis(scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition, withoutRotateTickText, tickCount) {
     var $$ = this.owner, config = $$.config,
         axisParams = {
             withOuterTick: withOuterTick,
             withoutTransition: withoutTransition,
-            tickTextRotate: withoutRotateTickText ? 0 : config.axis_y_tick_rotate
+            tickTextRotate: withoutRotateTickText ? 0 : config.axis_y_tick_rotate,
+            tickCount: tickCount
         },
         axis = c3_axis($$.d3, axisParams).scale(scale).orient(orient).tickFormat(tickFormat);
     if ($$.isTimeSeriesY()) {
@@ -275,10 +276,10 @@ Axis.prototype.getMaxTickWidth = function getMaxTickWidth(id, withoutRecompute)
         targetsToShow = $$.filterTargetsToShow($$.data.targets);
         if (id === 'y') {
             scale = $$.y.copy().domain($$.getYDomain(targetsToShow, 'y'));
-            axis = this.getYAxis(scale, $$.yOrient, config.axis_y_tick_format, $$.yAxisTickValues, false, true, true);
+            axis = this.getYAxis(scale, $$.yOrient, config.axis_y_tick_format, $$.yAxisTickValues, false, true, true, config.axis_y_tick_count);
         } else if (id === 'y2') {
             scale = $$.y2.copy().domain($$.getYDomain(targetsToShow, 'y2'));
-            axis = this.getYAxis(scale, $$.y2Orient, config.axis_y2_tick_format, $$.y2AxisTickValues, false, true, true);
+            axis = this.getYAxis(scale, $$.y2Orient, config.axis_y2_tick_format, $$.y2AxisTickValues, false, true, true, config.axis_y2_tick_count);
         } else {
             scale = $$.x.copy().domain($$.getXDomain(targetsToShow));
             axis = this.getXAxis(scale, $$.xOrient, $$.xAxisTickFormat, $$.xAxisTickValues, false, true, true);

src/c3.axis.js

@@ -25,10 +25,11 @@ function c3_axis(d3, params) {
         var start = domain[0], stop = domain[domain.length - 1];
         return start < stop ? [ start, stop ] : [ stop, start ];
     }
-    function generateTicks(scale) {
+    function generateTicks(scale, count) {
         var i, domain, ticks = [];
         if (scale.ticks) {
-            return scale.ticks.apply(scale, tickArguments);
+            count = count ? [count] : tickArguments;
+            return scale.ticks.apply(scale, count);
         }
         domain = scale.domain();
         for (i = Math.ceil(domain[0]); i < domain[1]; i++) {
@@ -81,7 +82,7 @@ function c3_axis(d3, params) {
 
             var scale0 = this.__chart__ || scale, scale1 = this.__chart__ = copyScale();
 
-            var ticks = tickValues ? tickValues : generateTicks(scale1),
+            var ticks = tickValues ? tickValues : generateTicks(scale1, params.tickCount),
                 tick = g.selectAll(".tick").data(ticks, scale1),
                 tickEnter = tick.enter().insert("g", ".domain").attr("class", "tick").style("opacity", 1e-6),
                 // MEMO: No exit transition. The reason is this transition affects max tick width calculation because old tick will be included in the ticks.

src/config.js

@@ -124,6 +124,7 @@ c3_chart_internal_fn.getDefaultConfig = function () {
         axis_y_tick_values: null,        
         axis_y_tick_rotate: 0,
         axis_y_tick_count: undefined,
+        axis_y_tick_exact: true,
         axis_y_tick_time_value: undefined,
         axis_y_tick_time_interval: undefined,
         axis_y_padding: {},
@@ -139,6 +140,7 @@ c3_chart_internal_fn.getDefaultConfig = function () {
         axis_y2_tick_outer: true,
         axis_y2_tick_values: null,
         axis_y2_tick_count: undefined,
+        axis_y2_tick_exact: true,
         axis_y2_padding: {},
         axis_y2_default: undefined,
         // grid

src/core.js

@@ -525,10 +525,10 @@ c3_chart_internal_fn.redraw = function (options, transitions) {
     $$.y.domain($$.getYDomain(targetsToShow, 'y', xDomainForZoom));
     $$.y2.domain($$.getYDomain(targetsToShow, 'y2', xDomainForZoom));
 
-    if (!config.axis_y_tick_values && config.axis_y_tick_count) {
+    if (!config.axis_y_tick_values && config.axis_y_tick_count && config.axis_y_tick_exact) {
         $$.yAxis.tickValues($$.axis.generateTickValues($$.y.domain(), config.axis_y_tick_count));
     }
-    if (!config.axis_y2_tick_values && config.axis_y2_tick_count) {
+    if (!config.axis_y2_tick_values && config.axis_y2_tick_count && config.axis_y2_tick_exact) {
         $$.y2Axis.tickValues($$.axis.generateTickValues($$.y2.domain(), config.axis_y2_tick_count));
     }
 

src/scale.js

@@ -76,8 +76,8 @@ c3_chart_internal_fn.updateScales = function () {
 
     $$.xAxis = $$.axis.getXAxis($$.x, $$.xOrient, $$.xAxisTickFormat, $$.xAxisTickValues, config.axis_x_tick_outer);
     $$.subXAxis = $$.axis.getXAxis($$.subX, $$.subXOrient, $$.xAxisTickFormat, $$.xAxisTickValues, config.axis_x_tick_outer);
-    $$.yAxis = $$.axis.getYAxis($$.y, $$.yOrient, config.axis_y_tick_format, $$.yAxisTickValues, config.axis_y_tick_outer);
+    $$.yAxis = $$.axis.getYAxis($$.y, $$.yOrient, config.axis_y_tick_format, $$.yAxisTickValues, config.axis_y_tick_outer, undefined, undefined, config.axis_y_tick_count);
-    $$.y2Axis = $$.axis.getYAxis($$.y2, $$.y2Orient, config.axis_y2_tick_format, $$.y2AxisTickValues, config.axis_y2_tick_outer);
+    $$.y2Axis = $$.axis.getYAxis($$.y2, $$.y2Orient, config.axis_y2_tick_format, $$.y2AxisTickValues, config.axis_y2_tick_outer, undefined, undefined, config.axis_y2_tick_count);
 
     // Set initialized scales to brush and zoom
     if (!forInit) {