Tricky matching

[Han Norsenberg]

Hello everyone, I've been struggling with some matching for a while and really appreciate any suggestion. Thank you all very much for your help.

[Han Norsenberg]

There's 2 data sets. The first one has 1 X with many Ys

#	X	Y	Other vars
1	X0	Y0	....
2	X0	YY0
3	X1	Y0

Y0 can change to Y1 at t1, then change to Y2 at t2 and change again in some cases where t1 and t2 are between t0 and T.

The second data set has 1 Y with many Xs where the Y continue to be in the data set for a while after the time of change.

Date	Y	X	Other vars
t0	Y0	X0 X1 X2	.....
	YY0	X0 X1 X2
t1	Y0	X2 X3 X4
	Y1	X1 X3 X4
	YY0	X0 X2 X3
t2	Y1	X2 X4 X5
	Y2	X0 X3 X5

I want to identify the time that X appears in both data set and together with other vars. Ideally, the output should look something like this

Date	X	Matched	Other vars
t0	X0	Y0	...
t0	X0	YY0
t0	X1	Y0
t1	X1	Y1
t2	X0	Y2