gistfile1.js

var original =  {
	_id: "3f369ef",
	_rev: "rev-23421-12",
	brand: "bran and ed",
	sizes: [
		{ sku: "3925", US: 10, UK: 11 },
		{ sku: "4635", US: 9, UK: 10 }
	]
};

var tmpl = {
	id: "@._id",
	brand: "@.brand",
	sizes: "@.sizes[].US"
};

var sanitized = magic(original, tmpl);

sanitized === {
	id: "3f369ef",
	brand: "bran and ed",
	sizes: [ 10, 9 ]
}