D3 sort descending for multi-dimensional arrays

Question

data = [[1062, 732, 1327754], [12335, 7693, 109313934], [290, 450, 1768064]];

how can I sort by the third value of each array object in my data resulting in the descending sort value of

[[12335, 7693, 109313934], [290, 450, 1768064], [1062, 732, 1327754]]

I am trying to use the d3 method: data.sort(d3.descending);

Answer 1

You need to pass data.sort a comparison function that will access the third element in each array:

data.sort(function(a, b){ return d3.descending(a[2], b[2]); })

Here because data is a multi-dimensional array, both a and b will be arrays as well. Then

d3.descending(a[2], b[2])

performs the comparison of the third element in each array such that the results are returned in descending order.

Answer 2

and, if you want to add in a secondary sort so that if the third column values are equal you then sort on the second column:

data.sort(function(a, b) {
  if(a[2]===b[2]) {
    return d3.descending(a[1], b[1]);
  }
  return d3.descending(a[2], b[2]);
};