[R] Matching where the source file has one record/ subject and the to-be-matched file has multiple records/subect

[Bert Gunter]

... and related to Ravi's post, will there always be at least one date in
file 2 that matches every date in file 1?  And if there isn't, what action
should be taken?

-- Bert

On Thu, Jul 23, 2026 at 9:36 AM Ravi Varadhan via R-help <
r-help using r-project.org> wrote:

> This is a classic matching problem, I believe.  Based on your description,
> you are looking for a 1-to-1 nearest-neighbor match based on the absolute
> difference in dates, with the constraint that once a subject in File 2 is
> used, all of their records are discarded.
>
> Correct?
>
> There are two classical approaches: greedy matching and global optimal
> matching.  While the greedy approach is simple to implement and often
> works, it can sometimes get into trouble (i.e., run out of good matches).
> The optimal approach would use the Hungarian algorithm (e.g., LSAP function
> in the clue package) to find the combination of matches that results in the
> lowest total date difference across the entire dataset.
>
> Ravi
>
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