> with(YourDataFrame, tapply(`Effective Date`, `RULE COLUMNS`,
> function(x) x[which.max(x)]))
David pointed out that this will just return a table of dates. One
work around is:
do.call("rbind", by(DataFrame, DataFrame[, "RULE COLUMNS"],
function(x) x[which.max(x[, "Effective Date"]), ]))
but that is not very simple or elegant, and both David's and Bill's
options seem superior.
Josh
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