Get dataframe of animals where the most recent assay was not negative.

A PCR assay trumps an non-PCR assay so that if a PCR assay is negative and and non-PCR assay is non-negative, the animal is negative for that agent.

get_still_pos(sorted_df)

Arguments

sorted_df	dataframe sorted values of all assays.

Value

A dataframe with assays whose last value are non-negative.