I am trying to analyse financial data for two different periods. Period one
will have say, 10 people with a value. Period 2 will have say 14 people with
a value.
However some people in period 1 will have no value in period 2 and also some
people in period 2 were new in period 1 and so did not exist in period 1.

If I have two separate files for each period (i.e. period 1 has people and a
value and similarly for period 2), how can I create a list with column 1
being for all people form both periods and showing their values for periods 1
and 2 in columns 2 and 3 therefore enabling me to anylyse any trends