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st: merge and nearest value


From   Francesco <cariboupad@gmx.fr>
To   statalist@hsphsun2.harvard.edu
Subject   st: merge and nearest value
Date   Sun, 19 Aug 2012 01:22:15 +0200

Dear Statalist,

I wish again that you could help me with this particular merging problem...

Let say I have a dataset A as:

TYPE   DATE
A            2
A            5
A            20
B            10
B            2


and I have another dataset B as :


TYPE  Special_Date
A              2
A              6
A              20
A              22
B              5
B              6

The question is : I would like to obtain the difference between the
date of each observation in A and the closest special date in B with
the same type. In case of ties I would take the latest date of the
two.

For example I would obtain here

TYPE   DATE   Difference
A            2            0=2-2
A            5            -1=5-6
A            20            0=20-20
B            10           +4=10-6
B            2             -3=2-5


I was thinking of reshaping the dataset B in order to have the special
dates in column for each type, merging then on type with A, creating a
difference variable between the date and each special date, and taking
the minimum...
But this involves creating a lot of variables and maybe there is
something more simple ?

Many thanks for your suggestions,

Best Regards,
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