Re: st: merge and nearest value

[David Kantor <kantor.d@att.net>]

First, I presume that in A, TYPE and DATE uniquely identify observations.

I suggest you do a -joinby- on TYPE. This will create a large 
multitude of observations.
Then for each distinct TYPE and DATE combination, compute the 
difference and then select (by TYPE and DATE) the one with the 
minimal difference.
You can do appropriate sorting to break ties in the manner you desire.

HTH
--David

At 07:22 PM 8/18/2012, Francesco wrote:
> 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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