Compute a unique numeric id for each unique row in a data frame.
Properties:
order(id)
is equivalent to do.call(order, df)
rows containing the same data have the same value
if drop = FALSE
then room for all possibilites
id(.variables, drop = FALSE)
.variables |
list of variables |
drop |
drop unusued factor levels? |
a numeric vector with attribute n, giving total number of possibilities
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