Bubble chart support

[skateinmars]

Hello,

I want to add bubble charts support to Axlsx. This is a type of scatter chart (which is already supported) but has a third value (besides x and y coordinates) that determines the size of the point (named bubbleSize in the XML).

I can't seem to find any readable documentation about this in the spec so for now I'm manually converting a generated scatter chart to a bubble chart in LibreOffice and checking the diff between the two XML chart files. This is incredibly inefficient though. The main change needed seems to be a <c:bubbleSize> that has to be added in the <c:bubbleChart> tag.

On the code side, I'm guessing we need to add a BubbleChart class and maybe a BubbleSeries class? The API should look like this:

chart.add_series xData: sheet["A1:A3"],
                         yData: sheet["B1:B3"],
                         bubbleSize: sheet["C1:C3"]

Am I on the right track here? Do you have any (usable) resource concerning the spec?

Anyway, thanks for this library, this is a great time saver.

[randym]

Hi @skateinmars conceptually you are definitely on the right track. I would suggest having a look at the specification. While the explanations are often less then helpful, the schema declarations are very helpful indeed.

http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-376,%20Fourth%20Edition,%20Part%201%20-%20Fundamentals%20And%20Markup%20Language%20Reference.zip

for example, page 4060 in Part 1 Fundamentals and Markup language reference:

<xsd:complexType name="CT_BubbleChart">
    <xsd:sequence>
       <xsd:element name="varyColors" type="CT_Boolean" minOccurs="0" maxOccurs="1"/>
       <xsd:element name="ser" type="CT_BubbleSer" minOccurs="0" maxOccurs="unbounded"/>
       <xsd:element name="dLbls" type="CT_DLbls" minOccurs="0" maxOccurs="1"/>
       <xsd:element name="bubble3D" type="CT_Boolean" minOccurs="0" maxOccurs="1"/>
       <xsd:element name="bubbleScale" type="CT_BubbleScale" minOccurs="0" maxOccurs="1"/>
       <xsd:element name="showNegBubbles" type="CT_Boolean" minOccurs="0" maxOccurs="1"/>
       <xsd:element name="sizeRepresents" type="CT_SizeRepresents" minOccurs="0" maxOccurs="1"/>
       <xsd:element name="axId" type="CT_UnsignedInt" minOccurs="2" maxOccurs="2"/>
       <xsd:element name="extLst" type="CT_ExtensionList" minOccurs="0" maxOccurs="1"/>
    </xsd:sequence>
</xsd:complexType>

[skateinmars]

Thanks for the tips. I managed to generate a bubble chart, though I didn't include every possible optional elements (bubble3D, bubbleScale...)

Basically the BubbleSeries is almost identical to the ScatterSeries, the change being in the initialize method: @bubbleSize = NumDataSource.new({:tag_name => :bubbleSize, :data => options[:bubbleSize]}) unless options[:bubbleSize].nil?

There is also a small change needed in NumDataSource, and a BubbleChart class.

I'm planning to do a pull request for this, but I'm wondering if my BubbleSeries and BubbleChart classes should inherit from the base Series and Chart classes or I can directly inherit from ScatterSeries/ScatterChart?

[randym]

Hi @skateinmars

Keep at it!!

BubbleChart should definitely inherit from Chart, and generate its own series data as the specification is different.

[skateinmars]

Thanks, the pull request https://github.com/randym/axlsx/pull/254 should be complete now!

[randym]

Sorry mate, I'll try to get to this later tonight. Thanks for your patience.