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### A.8.3 Internal Match Window

Internal Match Window

The Internal Match Window allows you to perform matching between rows of the same table, grouping rows that have the same or similar values in specified columns and producing a new table as a result. It can be obtained by using the Internal Match () item in the Control Window's Joins menu.

You might want to use this functionality to remove all rows which refer to the same object from an object catalogue, or to ensure that only one entry exists for each object, or to identify groups of several "nearby" objects in some way.

The result is created from the Apparent versions of the tables being joined, so that any row subsets, hidden columns, or sorts currently in force will be reflected in the output. Progress information on the match, which may take some time, is provided in the logging window and by a progress bar at the bottom of the window. When it is completed, you will be informed by a popup window which indicates that a new table has been created. This table will be added to the list in the Control Window and can be examined, manipulated and saved like any other.

The window has the following parts:

Match Criteria box
  Allows you to define what counts as a match between two rows.
Column Selection box
  Allows you to select which table to operate on and which columns supply the matching coordinates.
Match Action box
  Allows you to select what will be done (what new table will be created) when the matching groups of rows have been identified.
Log Panel
  Displays progress as the match is taking place. The progress bar at the bottom of the window also provides an indication of how far through each stage processing has got.
Control buttons
  The Go button starts the search when you are happy with the selections that you have made, and the Stop button interrupts it midway if you decide you no longer want the results (closing the Match Window also interrupts the calculation).

When considering matching beyond pairs, see the comments in Section 5.4 about the semantics of multi-object matches.

For information on the Tuning Parameters (), Full Profiling () and Parallel Execution () toolbar buttons, see Appendix A.8.1.3.

- A.8.3.1 Internal Match Action Box

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk