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The Internal Match Action box gives a list of options for what
will happen when an internal match calculation has completed.
In each case a new table will be
created as a result of the match. The options for what it will look like
are these:
-
Mark Groups of Rows
- The result is a table the same as the input table but with two
additional columns: GroupID and GroupSize.
Each group of rows which matched is assigned a unique integer,
recorded in the GroupId column, and the size of each group is
recorded in the GroupSize column.
Rows which don't match any others (singles) have null values in
both these columns.
So for example by sorting the resulting table
on GroupID you can group rows that match next to each other;
or by sorting on GroupSize you can see all the pairs, followed by
all the triples, ...
You can use this information in other ways, for instance if you
create a new Row Subset using the expression
"GroupSize == 5
" you could select only those
rows which form part of 5-object clusters.
-
Eliminate All Grouped Rows
- The result is a new table containing only "single" rows, that is
ones which don't match any other rows in the table according to the
match criteria. Any rows which match are thrown out.
-
Eliminate All But First of Each Group
- The result is a new table in which only one row (the first in the
input table order) from each group of matching ones is retained.
A subsequent internal match with the same criteria would therefore
show no matches.
-
New Table With Groups of Size N
- The result is a new "wide" table consisting of matched rows in
the input table stacked next to each other.
Only groups of exactly N rows in the input table are used to
form the output table; each row of the output table consists of
the columns of the first group member, followed by the columns of
the second group member and so on. The output table therefore has
N times as many columns as the input table.
The column names in the new table have "_1", "_2", ...
appended to them to avoid duplication.
Next Previous Up Contents
Next: Activation Window
Up: Internal Match Window
Previous: Internal Match Window
TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note
253
TOPCAT web page:
http://www.starlink.ac.uk/topcat/
Author email:
m.b.taylor@bristol.ac.uk