mapbox gl data driven styles (choropleth maps) - mapbox-gl-js

Question

I'm trying to create a choropleth map using mapbox-gl. In the example choropleth maps, it looks like they set the feature's paint fill colour based on the properties of the feature. Is there a way to set the colour by accessing a map?
ie. I have tiles each with a unique id in the feature property called id. I also have a json which maps each id with a value and would like to access those values to set the colour.
Is this possible? or am i limited to only being able to access values in the feature properties?

Answer 1

I'm not entirely sure if I understood your question correctly. But I think what you are trying to achieve can be done with expressions:
const geojson = {
type: 'FeatureCollection',
features: [
{
type: 'Feature',
properties: {
id: 'foo'
},
geometry: {
/* */
}
}
]
};
const values = {
foo: 'green',
bar: 'red',
baz: 'blue'
};
map.addLayer({
// ...
paint: {
'fill-color': [
[
'get',
// get the id property and use it as a key into "values"
['get', 'id'],
values
]
]
}
});
See the get expression: https://www.mapbox.com/mapbox-gl-js/style-spec#expressions-get

Answer 2

Update from 04.2018:
Since some moment constructions like
[
'get',
// get the id property and use it as a key into "values"
['get', 'id'],
values
]
stopped to work. The following exception occures: 'Bare objects invalid. Use ["literal", {...}]'. Now it is necessary to use type expressions, like this:
[
'get',
['string', ['get', 'id'],
['literal', values]
]
See this and this for reference.