public static <A> Map<String,BigDecimal> groupSum(Iterable<A> col,
			F1<A, String> groupF,
			F1<A, ? extends Number> valF) {
		HashMap<String, BigDecimal> result = new HashMap<String, BigDecimal>();
		for (A a : col) {
			String group = groupF.e(a);
			Number val = valF.e(a);
			MathUtil.increaseBig(group, val, result);
		}
		return result;
	}