The data returned from covidcast_signal() or covidcast_signals() can, if
called with the issues argument, contain multiple issues for a single
observation in a single location. These functions filter the data frame to
contain only the earliest issue or only the latest issue.
latest_issue(df)
earliest_issue(df)A covidcast_signal or covidcast_signal_long data frame, such as
returned from covidcast_signal() or the "long" format of
aggregate_signals().
A data frame in the same form, but with only the earliest or latest issue of every observation. Note that these functions sort the data frame as part of their filtering, so the output data frame rows may be in a different order.