Method observe

src/com/winvector/util/StatMap.java:23–31

Invariant: key set calls all keys ever observed (even those with net-zero count)

(final String key, final double x, final double wt)

	 * Invariant: key set calls all keys ever observed (even those with net-zero count)
	 */
	public void observe(final String key, final double x, final double wt) {
		SimpleStat v = counts.get(key);
		if(v==null) {
			v = new SimpleStat();
			counts.put(key,v);
		}
		v.sumW += wt;
		v.sumWX += wt*x;
	}

	public void observe(final String key, final SimpleStat val) {
		SimpleStat v = counts.get(key);