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## B.40 `tmatch1`: Performs a crossmatch internal to a single table

`tmatch1` performs efficient and flexible crossmatching between the rows of a single table. It can match rows on the basis of their relative position in the sky, or alternatively using many other criteria such as separation in in some isotropic or anisotropic Cartesian space, identity of a key value, or some combination of these; the full range of match criteria is dicussed in Section 7.1.

The basic task performed by the intra-table matcher is to identify groups of rows within the table which match each other. See Section 7.2 for an explanation of exactly what consitutes a match group. The result of identifying these groups is expressed as an output table in one of a variety of ways, specified by the `action` parameter. These options include marking group membership in added columns and eliminating some or all rows which form part of a match group.

- B.40.1 Usage
- B.40.2 Examples

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STILTS - Starlink Tables Infrastructure Library Tool Set
Starlink User Note256
STILTS web page: http://www.starlink.ac.uk/stilts/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk