I think I must be missing something obvious, but I'm having trouble
getting a data transformation to work on groupings of data within a data
frame (csss3) as defined by 2 factors (population, locid). The data are
sorted by year within locid within population and I want to lag another
variable (dbc), i.e, shift them down by 1 row replacing the first row with
NA, within groups defined by locid nested within population. I thought I
could do something using by(csss3,list(locid, population), function) but
don't seem to be having any success. Any suggestions??
Brian
Brian S. Cade
U. S. Geological Survey
Fort Collins Science Center
2150 Centre Ave., Bldg. C
Fort Collins, CO 80526-8818
email: [EMAIL PROTECTED]
tel: 970 226-9326
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