Would this work ?
d3.csv("file.csv", function(data) {
[...]
// Called each time there is an action on the dropdown menu
function updateGraph() {
// Select only data that are tagged with a certain category
var dataset = data.filter(function(d) { return d.category == selectedCategory; });
// Update graph visualization
}
}
This way you wouldn't have to reload your csv file each time.