Sorting objects based on property value in D3

Question

I have a array of objects for use in D3 e.g

var cities = [
  { city: "London", country: "United Kingdom", index: 280 },
  { city: "Geneva", country: "Switzerland", index: 259 },
  { city: "New York City", country: "United States", index: 237 },
  { city: "Singapore", country: "Singapore", index: 228 },
  { city: "Paris", country: "France", index: 219 },
  { city: "San Francisco", country: "United States", index: 218 },
  { city: "Copenhagen", country: "Denmark", index: 217 },
  { city: "Sydney", country: "Australia", index: 215 },
  { city: "Hong Kong", country: "Hong Kong", index: 214 },
  { city: "Brisbane", country: "Australia", index: 208 }
}

I would like to order the objects in ascending order based on their cities.index property. So that I can display them as such in D3.js. Im sure there is a way of doing this in D3 but I am yet to figure it out when dealing with an array of objects.

Any help?

Solution 1

You can pass an anonymous function to the Javascript Array.prototype.sort to sort by index. D3 has a function d3.ascending (v 3.x) that makes it easy to sort ascending:

cities.sort(function(x, y){
   return d3.ascending(x.index, y.index);
})

And here's the output:

[
 {"city":"Brisbane","country":"Australia","index":208},
 {"city":"Hong Kong","country":"Hong Kong","index":214},
 {"city":"Sydney","country":"Australia","index":215},
 {"city":"Copenhagen","country":"Denmark","index":217},
 {"city":"San Francisco","country":"United States","index":218},
 {"city":"Paris","country":"France","index":219},
 {"city":"Singapore","country":"Singapore","index":228},
 {"city":"New York City","country":"United States","index":237},
 {"city":"Geneva","country":"Switzerland","index":259},
 {"city":"London","country":"United Kingdom","index":280}
]

Solution 2

Just sort the array before you use it in D3, as Travis J mentioned in a comment. There's no reason to use D3 to sort (d3.ascending is just a comparison wrapper anyway).

Also, note that you have a } where you want a ] at the end of your declaration.

---

You can access each object's properties as so:

cities.sort(function(a, b){
    return a["index"]-b["index"];
});

Comments

[Travis J]

Why not just sort them in the array before using it?

[Casey Falk]

Just pass .sort() a custom sorting function. You can access the index property of the objects and use to determine order. javascriptkit.com/javatutors/arraysort.shtml

[Sam Mason]

@TravisJ Ideally this is what I would like to do sorry for not being more descriptive

[Casey Falk]

Why stringify the results? You don't really need it. :)

[mdml]

Just so the output in my console doesn't say [Object, Object, Object, ...]. But yeah, perhaps doesn't need to be in my answer.

[tyleha]

What if some array objects have undefined values? It doesn't appear that d3 sort deals with these cases.