beginAtZero support for logarithmic (#7862)

src/scales/scale.logarithmic.js

@@ -64,6 +64,7 @@ export default class LogarithmicScale extends Scale {
 	parse(raw, index) {
 		const value = LinearScaleBase.prototype.parse.apply(this, [raw, index]);
 		if (value === 0) {
+			this._zero = true;
 			return undefined;
 		}
 		return isFinite(value) && value > 0 ? value : NaN;
@@ -101,6 +102,11 @@ export default class LogarithmicScale extends Scale {
 		if (max <= 0) {
 			max = Math.pow(10, Math.floor(log10(min)) + 1);
 		}
+		// if data has `0` in it or `beginAtZero` is true, and min (non zero) value is at bottom
+		// of scale, lower the min bound by one exp.
+		if (!me._userMin && me._zero && min === Math.pow(10, Math.floor(log10(me.min)))) {
+			min = Math.pow(10, Math.floor(log10(min)) - 1);
+		}
 		me.min = min;
 		me.max = max;
 	}
@@ -153,6 +159,7 @@ export default class LogarithmicScale extends Scale {
 
 		me._startValue = log10(start);
 		me._valueRange = log10(me.max) - log10(start);
+		me._zero = me.options.beginAtZero;
 	}
 
 	getPixelForValue(value) {

test/specs/scale.logarithmic.tests.js

@@ -478,7 +478,7 @@ describe('Logarithmic Scale tests', function() {
 		});
 
 		var y = chart.scales.y;
-		expect(y.min).toBe(1);
+		expect(y.min).toBe(0.1);
 		expect(y.max).toBe(2);
 	});
 
@@ -508,7 +508,7 @@ describe('Logarithmic Scale tests', function() {
 		});
 
 		var y = chart.scales.y;
-		expect(y.min).toBe(1);
+		expect(y.min).toBe(0.1);
 		expect(y.max).toBe(2);
 	});
 
@@ -638,7 +638,7 @@ describe('Logarithmic Scale tests', function() {
 			type: 'line',
 			data: {
 				datasets: [{
-					data: [10, 5, 1, 25, 0, 78]
+					data: [10, 5, 1.1, 25, 0, 78]
 				}],
 				labels: []
 			},
@@ -751,7 +751,7 @@ describe('Logarithmic Scale tests', function() {
 						min: 0
 					}
 				},
-				firstTick: 1,
+				firstTick: 0.1,
 				describe: 'all stacks are defined and min: 0'
 			},
 			{
@@ -762,7 +762,7 @@ describe('Logarithmic Scale tests', function() {
 						min: 0
 					}
 				},
-				firstTick: 1,
+				firstTick: 0.1,
 				describe: 'not stacks are defined and min: 0'
 			},
 			{
@@ -783,7 +783,7 @@ describe('Logarithmic Scale tests', function() {
 						min: 0
 					}
 				},
-				firstTick: 1,
+				firstTick: 0.1,
 				describe: 'all stacks are defined and min: 0'
 			},
 			{
@@ -794,7 +794,7 @@ describe('Logarithmic Scale tests', function() {
 						min: 0
 					}
 				},
-				firstTick: 1,
+				firstTick: 0.1,
 				describe: 'not all stacks are defined and min: 0'
 			},
 		];
@@ -812,7 +812,8 @@ describe('Logarithmic Scale tests', function() {
 				chartEnd = 'top';
 			}
 			scaleConfig[setup.axis] = {
-				type: 'logarithmic'
+				type: 'logarithmic',
+				beginAtZero: false
 			};
 			Object.assign(scaleConfig, setup.scale);
 			scaleConfig[setup.axis].type = 'logarithmic';