Mapbox JS Runtime Styling from collection - mapbox

Question

So I have a Mapbox Tileset I've uploaded with census-block information for the US. Each geometry in the tileset has a property called GeoID, that I am trying to apply a style to based on another collection I have.
The collection is an array objects with this format: [{geoid: string, weight: number}, {geoid: string, weight: number},...]
I want to match the GeoIDs from the array to the layer from the tileset and color it based on the corresponding weight property from that object. Weight is a number between 0 and 1. I have tried searching the documentation on runtime styling and expressions from Mapbox, but I can't find anything about extrapolating data from a collection and conditionally applying it to the right geometries from a tileset.

Answer 1

You can generate an expression from your list of weights and than pass it to the layer your want to style:
const weights = [
{geoid: 1, weight: 10},
{geoid: 2, weight: 5},
{geoid: 3, weight: 30},
];
const cases = weights.map(weight => {
const condition = ['==', ['get', 'geoid'], weight.geoid];
const output = getColor(weight.weight);
return [
condition,
output
];
});
const expresion = ['case',
...cases.reduce((flat, conditionAndOutput) => [...flat, ...conditionAndOutput]),
'<default-color>'
];
/*
Will result in:
[
"case",
[
"==",
[
"get",
"geoid"
],
1
],
"rgb(255, 255, 255)",
[
"==",
[
"get",
"geoid"
],
2
],
"rgb(255, 255, 255)",
[
"==",
[
"get",
"geoid"
],
3
],
"rgb(255, 255, 255)",
"<default-color>"
]
*/