d3.scale on JSON Data

Question

I would like to enable domain and range finding on JSON data with D3. I can easily do so with hard-coded numbers but I'm unsure what I should do for JSON data I'm looking for.

For hard-coded numbers, I can easily get something I'm looking for:

var test = d3.scale.linear()
    .domain([200,1000]);

console.log(test(900)); // returns an obvious value adjusted for scale

But for a JSON Object I'm getting an error "cannot read property map of undefined" in my console. Obviously user error:

var test = d3.scale.linear()
    .domain(testData['Sources']['Value']);

console.log(test(900)); // returns "cannot read property 'map' of undefined

Should I somehow be doing a for-each on the JSON data, or D3's .enter() method?

Answer 1

You indeed need to iterate over the elements in your data, but D3 offers functions that make this easier. For example:

var test = d3.scale.linear()
    .domain(d3.extent(testData, function(d) { return d['Sources']['Value']; }));

This tells D3 to get ['Sources']['Value'] for every element in testData and return the min and max values in an array. I'm assuming that this is the format of your data, if not, adjust appropriately.