Some past threads have pointed out that lists can be used as dictionaries storing data with an associated key (environments do this too). I have the seemingly simpler case with integer values for the indices--however, the integers are not necessarily contiguous low numbers. My concern is that if id is 3000 then d <- list() d[[id]] <- some data and later retrieval with d[[id]] is going to be wasteful (e.g., produce something with 3000 elements). I could turn id into a string, but that seems pretty indirect. Is there any problem with the naive scheme outlined above? If so, what's a good way around it? -- Ross Boylan wk: (415) 514-8146 185 Berry St #5700 ross at biostat.ucsf.edu Dept of Epidemiology and Biostatistics fax: (415) 514-8150 University of California, San Francisco San Francisco, CA 94107-1739 hm: (415) 550-1062