Using d3js sort an array of arrays

Question

I have an array where each element in the array (representing a Supreme Court Chief Justice) contains an array of data points (the Chief Justice's name, number of disputes and year).

For each element in the top-level array, I need to sort the lower-level array in ascending order by year.

I attempted to sort year by ascending order using the following:

  nested_data.forEach(function(d) {
    d.values.sort(d3.ascending(d.values.year));
  });

But it did not sort the lower-level array in ascending order by year.

Here is the console.log of my nested data to show its structure.

Array[5]
  0:Object
    key:"Vinson"
    values:Array[7]
      0:Object
        chief:"Vinson"
        disputes:142
        year:Tue Jan 01 1946 00:00:00 GMT+0800 (CST)
      1:Object
      2:Object
      3:Object
      4:Object
      5:Object
      6:Object
  1:Object
    key:"Warren"
    values:Array[16]
  2:Object
    key:"Burger"
    values:Array[17]
  3:Object
    key:"Rehnquist"
    values:Array[19]
  4:Object
    key:"Roberts"
    values:Array[11]

How can I sort the lower-level array in ascending order by year?

Gerardo Furtado · Accepted Answer · 2016-12-20 00:25:28Z

This is the function:

nested_data.forEach(function(d) {
    d.values.sort(function(a, b) {
        return d3.ascending(+a.year, +b.year)
    });
});

Your original function had two problems:

Since you're sorting the values arrays, you don't need to repeat values in the compareFunction
When specified, compareFunction uses two parameters, normally named a and b. You have to put d3.ascending inside compareFunction. Have a look here.

Here is a demo with a bogus data:

var data = [{
        key: "foo",
        values: [{
            chief: "Bob",
            year: 1982
        }, {
            chief: "Tom",
            year: 1977
        }, {
            chief: "Carla",
            year: 2010
        }, {
            chief: "Ana",
            year: 1999
        }]
    }, {
        key: "bar",
        values: [{
            chief: "Bill",
            year: 2009
        }, {
            chief: "Ted",
            year: 2014
        }]
    }, {
        key: "baz",
        values: [{
            chief: "Fred",
            year: 1998
        }, {
            chief: "Su",
            year: 1992
        }, {
            chief: "Charlie",
            year: 1999
        }, {
            chief: "Alice",
            year: 1979
        }]
    }, ];

    data.forEach(function(d) {
        d.values.sort(function(a, b) {
            return d3.ascending(+a.year, +b.year)
        });
    });

    console.log(data);

<script src="https://d3js.org/d3.v4.min.js"></script>

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