Better automatic y-labelling.

Author: oesmith

lib/morris.grid.coffee

@@ -161,31 +161,14 @@ class Morris.Grid extends Morris.EventEmitter
       @ymax += 1
 
     if @options.axes is true or @options.grid is true
-      # calculate grid placement
-      span = @ymax - @ymin
-      ymag = Math.floor(Math.log(span) / Math.log(10))
-      unit = Math.pow(10, ymag)
-
-      # calculate initial grid min and max values
-      gmin = Math.round(@ymin / unit) * unit
-      gmax = Math.round(@ymax / unit) * unit
-      step = (gmax - gmin) / (@options.numLines - 1)
-
-      # ensure zero is plotted where the range includes zero
-      if gmin < 0 and gmax > 0
-        gmin = Math.round(@ymin / step) * step
-        gmax = Math.round(@ymax / step) * step
-
-      # special case for decimal numbers
-      if step < 1
-        smag = Math.floor(Math.log(step) / Math.log(10))
-        @grid = for y in [gmin..gmax] by step
-          parseFloat(y.toFixed(1 - smag))
+      if @options.ymax == @defaults.ymax and @options.ymin == @defaults.ymin
+        # calculate 'magic' grid placement
+        @grid = @autoGridLines(@ymin, @ymax, @options.numLines)
+        @ymin = Math.min(@ymin, @grid[0])
+        @ymax = Math.max(@ymax, @grid[@grid.length - 1])
       else
-        @grid = (y for y in [gmin..gmax] by step)
-
-      @ymin = gmin
-      @ymax = gmax
+        step = (@ymax - @ymin) / (@options.numLines - 1)
+        @grid = (y for y in [@ymin..@ymax] by step)
 
     @dirty = true
     @redraw() if redraw
@@ -205,6 +188,33 @@ class Morris.Grid extends Morris.EventEmitter
     else
       boundaryOption
 
+  autoGridLines: (ymin, ymax, nlines) ->
+    span = ymax - ymin
+    ymag = Math.floor(Math.log(span) / Math.log(10))
+    unit = Math.pow(10, ymag)
+
+    # calculate initial grid min and max values
+    gmin = Math.floor(ymin / unit) * unit
+    gmax = Math.ceil(ymax / unit) * unit
+    step = (gmax - gmin) / (nlines - 1)
+    if unit == 1 and step > 1 and Math.ceil(step) != step
+      step = Math.ceil(step)
+      gmax = gmin + step * (nlines - 1)
+
+    # ensure zero is plotted where the range includes zero
+    if gmin < 0 and gmax > 0
+      gmin = Math.floor(ymin / step) * step
+      gmax = Math.ceil(ymax / step) * step
+
+    # special case for decimal numbers
+    if step < 1
+      smag = Math.floor(Math.log(step) / Math.log(10))
+      grid = for y in [gmin..gmax] by step
+        parseFloat(y.toFixed(1 - smag))
+    else
+      grid = (y for y in [gmin..gmax] by step)
+    grid
+
   _calc: ->
     w = @el.width()
     h = @el.height()

morris.js

@@ -0,0 +1,25 @@
+describe 'Morris.Grid#autoGridLines', ->
+
+  beforeEach ->
+    @subject = Morris.Grid.prototype.autoGridLines
+
+  it 'should draw at fixed intervals', ->
+    @subject(0, 4, 5).should.deep.equal [0, 1, 2, 3, 4]
+    @subject(0, 400, 5).should.deep.equal [0, 100, 200, 300, 400]
+
+  it 'should pick intervals that show significant numbers', ->
+    @subject(102, 499, 5).should.deep.equal [100, 200, 300, 400, 500]
+
+  it 'should draw zero when it falls within [ymin..ymax]', ->
+    @subject(-100, 300, 5).should.deep.equal [-100, 0, 100, 200, 300]
+    @subject(-50, 350, 5).should.deep.equal [-125, 0, 125, 250, 375]
+    @subject(-400, 400, 5).should.deep.equal [-400, -200, 0, 200, 400]
+    @subject(100, 500, 5).should.deep.equal [100, 200, 300, 400, 500]
+    @subject(-500, -100, 5).should.deep.equal [-500, -400, -300, -200, -100]
+
+  it 'should generate decimal labels to 2 significant figures', ->
+    @subject(0, 1, 5).should.deep.equal [0, 0.25, 0.5, 0.75, 1]
+    @subject(0.1, 0.5, 5).should.deep.equal [0.1, 0.2, 0.3, 0.4, 0.5]
+
+  it 'should use integer intervals for intervals larger than 1', ->
+    @subject(0, 9, 5).should.deep.equal [0, 3, 6, 9, 12]

morris.min.js

@@ -197,3 +197,12 @@ describe 'Morris.Grid#setData', ->
     line.data.length.should.equal 0
     line.setData([{x: 2, y: '12'}, {x: 1, y: '13.5'}, {x: 4, y: '14'}, {x: 3, y: '16'}])
     line.data.length.should.equal 4
+
+  it 'should automatically choose significant numbers for y-labels', ->
+    line = Morris.Line
+      element: 'graph',
+      data: [{x: 1, y: 0}, {x: 2, y: 3600}]
+      xkey: 'x'
+      ykeys: ['y']
+      labels: ['y']
+    line.grid.should == [0, 1000, 2000, 3000, 4000]