how to filter a JSON file? (NYC Census Tracts) - json

Question

I am adapting an existing D3JS map-drawing file to work with a different JSON file. In the file 'ny.json' there are things called "objects" and inside of those there are things called "tracts" so I get how the references work for the current (working) code, which comes from here and looks like:
d3.json("./shapefiles/ny.json", function(error, ny) {
if (error) throw error;
var tracts = ny.objects.tracts;
tracts.geometries = tracts.geometries
.filter(function(d) { return (d.id / 10000 | 0) !== 99; });
svg.append("g")
.selectAll("path")
.data(topojson.feature(ny, tracts).features)
.enter().append("path")
.attr("class", "tract")
.attr("d", path)
However, the new JSON file doesn't have those 'objects' or 'tracts' and I'm trying to figure out how to filter it so that it can be used to draw a map not of New York State (as in the first one) but just of the Bronx county. It's possible that the two files are too different in structure that an easy filter change isn't possible, but I thought I would ask in case there's another solution. I haven't seen the 'meta' features in json before.

Answer 1

I am afraid it is not possible to display only Bronx in the map because census tract ids in ny.json are unique only at borough level. For instance, census tract 014300 appears in Bronx, Brooklyn, Manhattan, and Queens. ny.json stores only census tract ids in ny.objects.tracts.id, and not their FIPS County Codes.
This makes filtering on Borough name impossible: https://bl.ocks.org/memoryfull/ba6121d19f80f85f0beb
Even if the filtering was feasible, it would be suboptimal. Instead, I would create own GeoJSON of Bronx in any GIS software with census tract ids and then call it in your d3 code.