Assuming that your identifiers run 1 up, then here is one way:
local N = _N
expand `N'
bysort ID : gen ID2 = _n
gen DeltaN = .
qui forval i = 1/`N' {
su N if ID == `i', meanonly
replace DeltaN = N - r(mean) if ID2 == `i'
}
If your identifiers do not run 1 up, use -egen, group()- to get new
identifiers that do.
Also note
FAQ . . . . . . . . . . . . . . . Expanding datasets to all possible
pairs
2/03 How do I produce a dataset based on all possible
pairs of identifiers within each group?
http://www.stata.com/support/faqs/data/pairs.html
Nick
[email protected]
Cesare Fracassi
I have a db that looks like this:
ID N
1 1
2 0
3 4
4 2
5 2
6 0
.........
10 1
(the actual db is much larger than that)
I would like to create a new dataset that contains the nxn possible
combinations of observations and takes the differences between the Ns:
ID1 ID2 DeltaN
1 1 0
1 2 1
1 3 -3
1 4 -1
........................
1 10 0
2 1 -1
2 2 0
2 3 -4
.......
and so on for the nxn possible combinations...
any idea how to code that in stata?
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