Hi,
I have a time series data set as follows.
ID year P_t-1 P_t
1 1990 16 16
1 1991 16 16
1 1996 16 16
1 2005 42 42
1 2006 42 42
1 2007 42 42
2 1990 29 29
2 1991 29 29
2 1992 29 29
Where P_t and P_t-1 represents price in year t and t-1 respectively.
What I wish to achieve is to create a new variable "Change". This
variable should show the number of years passed since the last change
in P_t. In the above example the data should finally look like below.
ID year P_t-1 P_t Change
1 1990 . 16 0
1 1991 16 16 1
1 1996 16 16 2
1 1997 16 16 3
1 2005 16 42 0
1 2006 42 42 1
1 2007 42 42 2
2 1990 . 29 0
2 1991 29 29 1
2 1992 29 29 2
2 1993 29 35 0
If I do
bysort ID P_t : gen Change=_n-1 I get the varible numbered but it
doesnt sort the year. If I sort ID and year then I cant use the _n to
generate these numbers.
Can someone help me with this?
Thanks in advance,
Rijo.
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