flattens JS object hierarchies (used for shaping data for D3.js)

flatten_objs.js

//
// flattens object hierarchies like {'US': {'AZ': {size: 999, ...} } }
// into array of "rows" like {country: 'US', state: 'AZ': size: 999, ...}
//     e.g. flatten(data, 2, ['country', 'state'])
//
// values can also form another level like so:
//     e.g. flatten(data, 3, ['country', 'state', 'stat'])
// which produces: {country: 'US', state: 'AZ', stat: 'size', value: 999}
//
// NOTE: modifies objects directly, so don't run multiple times with diff levels
//
function flatten(obj, level, keys) {
	var keyname = keys.length > 0 ? keys[0] : null;

	if (level == 0) {
		if (!obj || obj.constructor != Object) {
			var obj2 = {};
			obj2[keyname || 'value'] = obj;
			obj = obj2;
		}
		return [obj];
	} else {
		var arr = [];
		for (var k in obj) {
			flatten(obj[k], level - 1, keys.slice(1))
				.forEach(function(o) {
					o[keyname] = k;
					arr.push(o);
				});
		}
		return arr;
	}
}