Sort ascending, by key

This would be so useful to have in D3:

d3.ascendingKey = function(key) {
   return function (a, b) {
      return a[key] < b[key] ? -1 : a[key] > b[key] ? 1 : a[key] >= b[key] ? 0 : NaN;
   };
}

Alternatively also supporting accessor functions, but I think that’s less often needed and possibly inefficient:

d3.ascendingKey = function(key) {
   return typeof key == 'function' ? function (a, b) {
          return key(a) < key(b) ? -1 : key(a) > key(b) ? 1 : key(a) >= key(b) ? 0 : NaN;
      } : function (a, b) {
          return a[key] < b[key] ? -1 : a[key] > b[key] ? 1 : a[key] >= b[key] ? 0 : NaN;
      };
}

[mbostock]

A shorter but slightly less efficient version:

d3.ascendingKey = function(key) {
  return function(a, b) {
    return d3.ascending(a[key], b[key]);
  };
};

In practice I tend to do things like:

array.sort(function(a, b) { return d3.ascending(a.foo, b.foo); });

[mbostock]

I’m not planning on adding these to 3.x, but hopefully 4.0’s module system will make it easier to bundle plugins like d3-jetpack.