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### A.3.4 Subsets Window

Subsets Window

The Subsets Window displays the Row Subsets which have been defined. You can display it using the Row Subsets () button when the chosen table is selected in the Control Window's Table List.

The subsets are displayed in a JTable widget with a row for each subset. The columns of the JTable are as follows:

_ID
  A unique and unchanging identifier for the subset, which consists of a "_" character (underscore) followed by an integer. This can be used to refer to it in expressions for synthetic columns or other subsets.

  Note: in previous versions of TOPCAT the hash sign ("#") was used instead of the underscore for this purpose; the hash sign no longer has this meaning.

Name
  A name used to identify the subset. It is ideally, but not necessarily, unique. It can be edited (double-click on the cell) to change the name.
Size
  The number of rows in this subset. This column is usually filled in when the subset is defined, but it is not guaranteed to remain correct if the table data change, since counting may be an expensive process so it is not automatically done with every change. If values in this column are blank or suspected incorrect, a recount can be forced by using the Count Subsets () button described below.
Fraction
  Shows the same information as the preceding Size column, but as a percentage of the total number of rows in the table.
Expression
  If the subset has been defined by an algebraic expression, this will be here. It can be edited (double-click on the cell) to change the expression.
Column $ID
  If the subset has been defined by equivalence with a boolean-valued column, this will show the $ID of the column that it came from (see Appendix A.3.3).

Entries in the Name and Expression columns can be edited by double-clicking on them in the normal way.

The following toolbar buttons are available in this window:

New Subset
  Pops up the Algebraic Subset Window to allow you to define a new subset algebraically.
Add Sample Subset
  Pops up a dialogue window to allow you to define a new subset consisting of every N'th row of the table.
Add Head Subset
  Pops up a dialogue window to allow you to define a new subset consisting of the first N rows of the table.
Add Tail Subset
  Pops up a dialogue window to allow you to define a new subset consisting of the last N rows of the table.
Remove Subset
  Deletes one of the subsets in the list. Once deleted, a subset cannot be recovered. Note that attempts to use its name or _ID in algebraic expressions which you add or modify in the future will fail, though its use in existing expressions will continue to work.
Invert Subset
  Creates a new subset which is the complement of the selected one. The new one will include all the rows which are excluded by the selected one (and vice versa). To use this action, first select a subset by clicking on its row in the JTable.
To Column
  If one of the rows in the JTable is selected, this will turn that subset into a new column. It will pop up the Synthetic Column Window, filled in appropriately to add a new boolean column to the table based on the selected subset. You can either accept it as is, or modify some of the fields. To use this action, first select a subset by clicking on its row in the JTable.
Count Subsets
  Counts how many rows are in each subset and displays this in the Size column. This forces a count or recount to fill in or update these values.
Broadcast Subset
  Causes the selected subset to be broadcast using SAMP or PLASTIC to other listening applications. Any other listening application which is displaying the same table is then invited to highlight the selection of rows corresonding to the selected subset. This option and the corresponding Send Subset to ... option are also available from the Interop menu. See Section 9 for more information about tool interoperability.

The following additional menu items are available:

Send subset to ...
  As for the Broadcast Subset item above, but sends the subset to only a single selected application. A submenu will give a list of all the currently registered applications which can make sense of a subset. If there are none, this item will be disabled.
Autocount rows
  Normally, the Size and Fraction columns of the displayed table (see above) are filled in as soon as a new subset is defined. However for very large tables this could be slow - if you want to prevent this autocounting you can deselect this menu item. In this case the Size and Fraction columns will only be filled in when the Count () button is hit or if TOPCAT finds out the size as the result of some other operation (such as plotting).

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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@bristol.ac.uk