Selecting the last year attended

[PDevi]

Hi all,

I have data as below, with employees attending conferences over a number of years. 

Data:

id      Year

1       2017   

1       2018

2       2017

2       2018

2       2019

2       2020

3       2019

I have to find the most recent year that the participant attended previously for each year. So, what I need is this:

Result needed:

id      Year        Previously_attended

1       2017       

1       2018       2017

2       2017       

2       2018       2017

2       2019       2018

2       2020       2019

3       2019

I can't figure out how to do this and would appreciate help. Thanks in advance for your time and patience.

[Reeza · Accepted solution]

LAG function.

data want;
set have;
by ID;
previously_attended = lag(year);
if first.id then call missing(previously_attended);
run;