Support min: / max: options for y-axis range

lib/squid.rb

@@ -27,6 +27,8 @@ module Interface
     # @option settings [Numeric] :steps (4) the number of gridlines.
     # @option settings [Boolean] :ticks (true) whether to plot the ticks.
     # @option settings [Symbol] :type (:column) the type of graph.
+    # @option settings [Numeric] :min
+    # @option settings [Numeric] :max
     def chart(data =  {}, settings = {})
       Graph.new(self, data, settings).draw
     end

lib/squid/axis.rb

@@ -7,8 +7,8 @@ class Axis
     include Format
     attr_reader :data
 
-    def initialize(data, steps:, stack:, format:, &block)
-      @data, @steps, @stack, @format = data, steps, stack, format
+    def initialize(data, steps:, stack:, format:, min: nil, max: nil, &block)
+      @data, @steps, @stack, @format, @min, @max = data, steps, stack, format, min, max
       @width_proc = block if block_given?
     end
 
@@ -40,13 +40,13 @@ def label_width(label)
 
     def min
       if @data.any? && values.first && values.first.any?
-        [values.first.min, 0].min
+        @min || [values.first.min, 0].min
       end
     end
 
     def max
       if @data.any? && values.last && values.last.any?
-        closest_step_to values.last.max
+        closest_step_to(@max || values.last.max)
       end
     end
 

lib/squid/configuration.rb

@@ -36,6 +36,10 @@ def self.integer
       -> (value) { value.to_i }
     end
 
+    def self.optional_integer
+      -> (value) { value && value.to_i }
+    end
+
     def self.symbol
       -> (value) { value.to_sym }
     end
@@ -62,6 +66,8 @@ def self.array(proc = nil)
       steps:        {as: integer,        default: '4'},
       ticks:        {as: boolean,        default: 'true'},
       type:         {as: symbol,         default: 'column'},
+      min:          {as: optional_integer, default: nil},
+      max:          {as: optional_integer, default: nil},
     }
 
     attr_accessor *ATTRIBUTES.keys

lib/squid/graph.rb

@@ -13,7 +13,7 @@ module Squid
   class Graph
     extend Settings
     has_settings :baseline, :border, :chart, :colors, :every, :formats, :height
-    has_settings :legend, :line_widths, :steps, :ticks, :type, :labels
+    has_settings :legend, :line_widths, :steps, :ticks, :type, :labels, :min, :max
 
     def initialize(document, data = {}, settings = {})
       @data, @settings = data, settings
@@ -96,7 +96,7 @@ def right
 
     def axis(first:, last:)
       series = @data.values[first, last].map(&:values)
-      options = {steps: steps, stack: stack?, format: formats[first]}
+      options = {steps: steps, stack: stack?, format: formats[first], min: min, max: max}
       Axis.new(series, options) {|label| @plot.width_of label}
     end
 

lib/squid/point.rb

@@ -9,11 +9,16 @@ def self.for(series, minmax:, height:, labels:, stack:, formats:)
       @max = Hash.new 0
       min, max = minmax
       offset = -> (value) { value * height.to_f / (max-min) }
+      y_offset = nil
       series.map.with_index do |values, series_i|
         values.map.with_index do |value, i|
-          h = y_for value, index: i, stack: false, &offset if value
-          y = y_for value, index: i, stack: stack, &offset if value
-          y = y - offset.call([min, 0].min) if value
+          if value
+            h = y_for value, index: i, stack: false, &offset
+            y = y_for value, index: i, stack: stack, &offset
+            y_offset ||= offset.call(min || 0) # only calculate this once, since the result will never change
+            y = y - y_offset
+          end
+
           label = format_for value, formats[series_i] if labels[series_i]
           new y: y, height: h, index: i, label: label, negative: value.to_f < 0
         end

spec/axis_spec.rb

@@ -76,6 +76,13 @@
         expect(labels).to eq %w(9.9 -5.1 -20 -35 -50)
       end
     end
+
+    describe 'given :min and :max' do
+      let(:options) { {steps: steps, stack: stack?, format: format, min: -500, max: 1000 } }
+      it "uses the give values as first and last label" do
+        expect(labels).to eq ["1,000", "625", "250", "-125", "-500"]
+      end
+    end
   end
 
   describe '#width' do

spec/point_spec.rb

@@ -59,5 +59,15 @@
         expect(points.last.map &:y).to eq [nil, 89.95, 0.0]
       end
     end
+
+    context "given a positive min" do
+      let(:minmax) { [100, 150] }
+      let(:series) { [[110.0, 100, 130.0], [nil, 120.0, 150.0]] }
+
+      it 'generates y values relative to the minimum' do
+        expect(points.first.map &:y).to eq [20.0, 0.0, 60.0]
+        expect(points.last.map &:y).to eq [nil, 40.0, 100.0]
+      end
+    end
   end
 end

spec/squid_spec.rb

@@ -241,6 +241,11 @@
       it { expect(colors_of(chart).fill_color).to eq [1.0, 0.0, 0.0] }
     end
 
+    describe 'uses a given range with max and min options' do
+      let(:settings) { options.merge(steps: 5, max: 100, min: -100).except(:format) }
+      it { expect(strings_of chart).to eq ["100", "60", "20", "-20", "-60", "-100"] }
+    end
+
     describe 'formats value labels with the value of the :format option' do
       let(:settings) { options.merge label: true, format: :percentage }
       it { expect(strings_of chart).to eq %w(50.0% -30.0% 20.0%) }