使用变量访问D3中的嵌套JSON键

Question

I am trying to figure out the best method for accessing nested json data in d3.

So my data looks something like this:

{
    "Florida":{"New York": "yellow",
                "New Jersey": "blue",
                "Pennsylvania": "green",
etc..

And my d3.select function looks something like:

    .selectAll("path")
.style('fill', function(d){
                                    return jsondata.state[d.properties.NAME];

of course, var state here is a variable, which should be referring to "Florida", but doesn't.

The way I see it, there are two ways:

1. Use some of the parsing methods outlined in this post . Namely, the .get() method

2. Use d3.nest() in some capacity and rolling up my data into an accessible object ahead of the .style function.

What is the best method?

Answer 1

You can use an ordinal scale, and change its domain and range based on whatever state is selected, and its data.

Create a scale without a domain or range:

var color = d3.scale.ordinal();

Then when a state is selected, get its name, and get the d3.entries for its corresponding object:

var entries = d3.entries(yourData[selectedState]);

Then set the domain and range of the scale to be the keys and values respectively:

color.domain(entries.map(function(d) {return d.key;}));
color.range(entries.map(function(d) {return d.value;}));

Finally, select all of your state paths and use the scale to set the fill:

.selectAll('path').attr('fill', function(d) {return color(d.properties.NAME)})