I have the following data

ID x y time
1  10 20 0
1  10 30 1
1 10 40 2
2 12 23 0
2 12 25 1
2 12 28 2
2 12 38 3
3 5 10 0
3 5 15 2
.....

x is time invariant, ID is the subject id number, y is changing over time.

I want to find out the difference between the first and last observed y
value for each subject and get a table like

ID x y
1 10 20
2 12 15
3 5 5
......

Is there any easy way to generate the data set?

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