Generic function to add an age column from an exact age column. Works for
both participant and contact data by specifying the column prefix.
If <prefix>_exact exists, it overwrites <prefix> with its values.
Otherwise, it creates <prefix> with NA values if it doesn't exist.
add_age(data, prefix)The data with the age column set from exact ages or initialised to NA
A data.table containing age data
Column name prefix: "part_age" for participants, "cnt_age" for contacts