Dynamically adjust bubble radius of counties? - d3.js

Question

Following the County Bubbles example, it's easy to add a bubble for each county. This is how it is added in the example:
svg.append("g")
.attr("class", "bubble")
.selectAll("circle")
.data(topojson.feature(us, us.objects.counties).features
.sort(function(a, b) { return b.properties.population - a.properties.population; }))
.enter().append("circle")
.attr("transform", function(d) { return "translate(" + path.centroid(d) + ")"; })
.attr("r", function(d) { return radius(d.properties.population); })
.append("title")
.text(function(d) {
return d.properties.name
+ "\nPopulation " + formatNumber(d.properties.population);
});
However, rather than using a variable from the json file (population), I need to update the radii according to a variable which dynamically changes (so I cannot put it in the json file beforehand as was done in the example). I call updateRadii() when a county is clicked, which needs access to the FIPS.
var currFIPS,
flowByFIPS;
var g = svg.append("g");
queue()
.defer(d3.json, "us.json")
.defer(d3.csv, "census.csv", function(d) {
return {
work: +d.workplace,
home: +d.residence,
flow: +d.flow
}
})
.await(ready);
function ready(error, us, commute) {
// Counties
g.append("g")
.attr("class", "counties")
.selectAll("path")
.data(topojson.feature(us, us.objects.counties).features)
.enter().append("path")
.attr("d", path)
.on("click", function(d) {
// Get FIPS of selected county
currFIPS = d.id;
// Filter on selected county (i.e., grab
// people who work in the selected county)
var data = commute.filter(function(d) {
return d.work == currFIPS;
});
// Create d3.map for where these people live
flowByFIPS = d3.map(data, function(d) {
return d.home;
});
// Update radii at "home" counties to reflect flow
updateRadii();
});
// Bubbles
g.append("g")
.attr("class", "counties")
.selectAll("circle")
.data(topojson.feature(us, us.objects.counties).features)
.enter().append("circle")
.attr("id", function(d) { return d.id; })
.attr("transform", function(d) {
return "translate(" + path.centroid(d) + ")";
})
.attr("r", 0); // invisible before a county is clicked
}
function updateRadii() {
svg.selectAll(".counties circle")
.transition()
.duration(300)
.attr("r", function(d) {
return flowByFIPS.get(d.id).flow
});
}
According to the error code, I believe that the circles do not have an id (FIPS code) attached. How do I get them to have an id? (I tried nesting the circle with the path using .each as explained in this answer, but could not get it working.)
Note that the above code works for updating fill on paths (rather than circles). For example, sub updateRadii(); for updateFill(); with the function as:
function updateFill() {
svg.selectAll(".counties path")
.transition()
.duration(300)
.attr("fill", function(d) {
return flowByFIPS.get(d.id).color; // e.g., "#444"
});
}

Answer 1

The problem here is that you don't supply d3 with data in the update function. I will recommend you update the data loaded from the file on the clicks, and from there you update the svg.
var update = function() {
g.selectAll(".country")
.data(data)
.attr("r", function(d) { return d.properties.flow_pct });
};
var data = topojson.feature(us, us.objects.counties).features;
data.forEach(function(x) { x.properties.flow_pct = /* calc the value */; })
g.append("g")
.attr("class", "counties")
.selectAll(".country")
.data(data)
.enter()
.append("circle")
.attr("class", "country")
.attr("transform", function(d) {
return "translate(" + path.centroid(d) + ")";
})
.on("click", function(d) {
// more code
data.forEach(function(x) { x.properties.flow_pct = /* calc the NEW value */; })
update();
});
update();
I've tried to use as much as the same code as before, but still trying to straiten it a bit out. The flow is now more d3-like, since the update function works on the changed data.
Another plus which this approach is both first render and future updates use the same logic for finding the radius.

Answer 2

It turns out to be an obvious solution. I forgot to check for the cases where a flow doesn't exist. The code above works if updateRadii() is changed to:
function updateRadii() {
svg.selectAll(".counties circle")
.transition()
.duration(300)
.attr("r", function(d) {
if (currFIPS == d.id) {
return 0;
}
var county = flowByFIPS.get(d.id);
if (typeof county === "undefined") {
return 0;
} else {
return county.flow;
}
});
}