Add config.axis_x_start option to start x ticks with some value

c3.js

@@ -1200,6 +1200,7 @@
             // axis
             axis_rotated: false,
             axis_x_show: true,
+            axis_x_start: 0,
             axis_x_type: 'indexed',
             axis_x_localtime: true,
             axis_x_categories: [],
@@ -4650,6 +4651,7 @@
             .style("text-anchor", $$.textAnchorForY2AxisLabel.bind($$));
     };
     c3_chart_internal_fn.getXAxis = function (scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition) {
+
         var $$ = this, config = $$.config,
             axisParams = {
                 isCategory: $$.isCategorized(),
@@ -4657,8 +4659,15 @@
                 tickMultiline: config.axis_x_tick_multiline,
                 tickWidth: config.axis_x_tick_width,
                 withoutTransition: withoutTransition,
-            },
-            axis = c3_axis($$.d3, axisParams, $$).scale(scale).orient(orient);
+            };
+
+        if(tickValues && config.axis_x_start){
+            tickValues = tickValues.map(function(x) {
+                return x + config.axis_x_start;
+            });
+        }
+
+        var axis = c3_axis($$.d3, axisParams, $$).scale(scale).orient(orient);
 
         if ($$.isTimeSeries() && tickValues) {
             tickValues = tickValues.map(function (v) { return $$.parseDate(v); });
@@ -4688,6 +4697,11 @@
         if (config.axis_x_tick_fit || config.axis_x_tick_count) {
             tickValues = $$.generateTickValues($$.mapTargetsToUniqueXs(targets), config.axis_x_tick_count, $$.isTimeSeries());
         }
+        if(tickValues && config.axis_x_start){
+            tickValues = tickValues.map(function(x) {
+                return x + config.axis_x_start;
+            });
+        }
         if (axis) {
             axis.tickValues(tickValues);
         } else {
@@ -8216,7 +8230,12 @@
             return !(id%divisor);
         }
         function generateTicks(scale) {
-            var i, domain, ticks = [];
+            var i, domain, ticks = [], startValue = 0;
+
+            if($$.isXAxis(orient) && $$.config.axis_x_start){
+                startValue = $$.config.axis_x_start;
+            }
+
             if (scale.ticks) {
                 return scale.ticks.apply(scale, tickArguments);
             }

spec/axis-spec.js

@@ -786,4 +786,47 @@ describe('c3 chart axis', function () {
         });
     });
 
+    describe('start with', function(){
+        it('should update args', function(){
+            args = {
+                data: {
+                    columns: [
+                        ['data1', 0, 1, 2, 3]
+                    ]
+                },
+                axis: {
+                    x: {
+                        show: true,
+                        start: 1
+                    }, 
+                    y: {
+                        show: true
+                    }
+                }
+            };
+
+            expect(true).toBeTruthy();
+        });
+
+        it('should start x ticks with axis_x_start', function(){
+            var xTickSpans = chart.internal.main.selectAll('.c3-axis-x g.tick text tspan')[0];
+            var yTickSpans = chart.internal.main.selectAll('.c3-axis-y g.tick text tspan')[0];
+
+            expect(xTickSpans[0].textContent).toBe('1');
+            expect(yTickSpans[0].textContent).toBe('0');
+        });
+
+        it('should work with load', function(){
+            chart.load({
+                columns: ['data2', 4, 5, 6]
+            });
+
+            var xTickSpans = chart.internal.main.selectAll('.c3-axis-x g.tick text tspan')[0];
+            var yTickSpans = chart.internal.main.selectAll('.c3-axis-y g.tick text tspan')[0];
+
+            expect(xTickSpans[0].textContent).toBe('1');
+            expect(yTickSpans[0].textContent).toBe('0');
+        });
+    });
+
 });

src/axis.js

@@ -31,6 +31,7 @@ c3_chart_internal_fn.initAxis = function(){
         .style("text-anchor", $$.textAnchorForY2AxisLabel.bind($$));
 };
 c3_chart_internal_fn.getXAxis = function (scale, orient, tickFormat, tickValues, withOuterTick, withoutTransition) {
+
     var $$ = this, config = $$.config,
         axisParams = {
             isCategory: $$.isCategorized(),
@@ -38,8 +39,15 @@ c3_chart_internal_fn.getXAxis = function (scale, orient, tickFormat, tickValues,
             tickMultiline: config.axis_x_tick_multiline,
             tickWidth: config.axis_x_tick_width,
             withoutTransition: withoutTransition,
-        },
-        axis = c3_axis($$.d3, axisParams, $$).scale(scale).orient(orient);
+        };
+
+    if(tickValues && config.axis_x_start){
+        tickValues = tickValues.map(function(x) {
+            return x + config.axis_x_start;
+        });
+    }
+
+    var axis = c3_axis($$.d3, axisParams, $$).scale(scale).orient(orient);
 
     if ($$.isTimeSeries() && tickValues) {
         tickValues = tickValues.map(function (v) { return $$.parseDate(v); });
@@ -69,6 +77,11 @@ c3_chart_internal_fn.updateXAxisTickValues = function (targets, axis) {
     if (config.axis_x_tick_fit || config.axis_x_tick_count) {
         tickValues = $$.generateTickValues($$.mapTargetsToUniqueXs(targets), config.axis_x_tick_count, $$.isTimeSeries());
     }
+    if(tickValues && config.axis_x_start){
+        tickValues = tickValues.map(function(x) {
+            return x + config.axis_x_start;
+        });
+    }
     if (axis) {
         axis.tickValues(tickValues);
     } else {

src/c3.axis.js

@@ -57,7 +57,12 @@ function c3_axis(d3, params, $$) {
         return !(id%divisor);
     }
     function generateTicks(scale) {
-        var i, domain, ticks = [];
+        var i, domain, ticks = [], startValue = 0;
+
+        if($$.isXAxis(orient) && $$.config.axis_x_start){
+            startValue = $$.config.axis_x_start;
+        }
+
         if (scale.ticks) {
             return scale.ticks.apply(scale, tickArguments);
         }

src/config.js

@@ -82,6 +82,7 @@ c3_chart_internal_fn.getDefaultConfig = function () {
         // axis
         axis_rotated: false,
         axis_x_show: true,
+        axis_x_start: 0,
         axis_x_type: 'indexed',
         axis_x_localtime: true,
         axis_x_categories: [],