在d3.js中处理可选数据

Question

How would you handle data where some parts are optional? For example this data:

[
    {
        width: 10,
        height: 20,
        margin: { top: 10, right: 10, bottom: 10: left: 10 }
    },
    {
        width: 10,
        height: 20
    }
]

So I'd like to only append some SVG rect when margin is available. I could use the visibility attribute to hide it, but this would mean I have unnecessary nodes and have to write null checking code to avoid javascript errors.

var svgobj = svg.selectAll('.object').data(objects);

var svgobjEnter = svgobj.enter().append('g')
    .attr('class', 'object');

svgobjEnter.append('rect')
    .attr('class', 'margin');
    .attr('width', function(d) { return d.width + d.margin.left + d.margin.right; })
    .attr('height', function(d) { return d.height + d.margin.top + d.margin.bottom; })

Answer 1

You can filter your data to do this:

svg.selectAll("rect")
   .data(objects.filter(function(d) { return d.margin != undefined; }))
   .enter()
   .append("rect")
// etc