Hi all,

I'm new to the list but have benfited from it quite extensively. Straight to
my rather strange question:

I have a data frame that contains mapping rules in this way:

ACCOUNT, RULE COLUMNS, Effective Date


The dataframe comes from a database that stores all dates. What I would like
to do is to create a data frame with only the most recent rule for each
account. In traditional programming languages I would loop through each
account find the most recent rule(s) and fill up my updated data frame.

Does anyone have any better idea to use R's magic (Its syntax is still
magical to me) for this problem?

By the way the list of rules is quite extensive (144643 lines to be
precise), and there are usually 1-3 most recent rules (rows) for each
account.

Thanks.

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