setting up time-to-event data given certain conditions.

[Lily07]

I want to make a table with multiple observations per participant given certain conditions.

The conditions are:

1) the follow-up starts when event 1 occurs for the first time 

2) The participant isn't included if event 1 does not occur.

3) the time to event is calculated between the first time for event 1 and the following firstevent 2.

4) If event 2 occurs prior to event 1, it isn't counted.

So below is the example tables:

What I have

id	event1	event2
1	20100108	.
1	.	20110108
2	.	20110305
2		20130110
3	.	20110510
3		20140510
3	20160510	.
4	20100210
4	20100310
4		20150220

What I want

id	event1	event2	censored	days
1	20100108	20110108	0	365.5
3	20160510	.	1	1827.5
4	20100210	20150220	0	1470

Could you please help me to write the code? 

Thank you very much.

[ChrisNZ]

Why is ID 3 in the output?