Using d3js sort an array of arrays - 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?

Answer 1

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>