The way to compare empirical distributions is to make cumulative distribution functions out of the raw data [use ecdf()] then compare them by plotting [via qqplot()]. And then use KS. Discreet distributions can have direct functions called probability mass functions. Continuous can not because any single realization instance (say 3.57867363474624) can not have a probability, only an interval can (say 3-4). You could compare histograms but ecdf are used far far more often.