.help tdiffer May92 tables
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NAME
tdiffer -- Create a new table which is the difference of two tables.
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USAGE
tdiffer intable1 intable2 outtable colnam1 colnam2
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DESCRIPTION
This task creates an output table containing all the rows of the first table
which do not match the rows in the second table.
The first, second, and output tables are given by the task
parameters 'intable1', 'intable2', and 'outtable' respectively.
The match is done on the columns specified by the task parameters 'colnam1'
and 'colnam2'.
Other columns are ignored.
If the two tables are disjoint, the output table will be a copy of
the first table, except the rows will be sorted.
If the first table is a subset of the second, the output table will be empty.
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PARAMETERS
.ls intable1 [file name]
The name of the first input table.
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.ls intable2 [file name]
The name of the second input table.
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.ls outtable [file name]
The name of the output table.  The output table has the same header parameters
and column names as the first table. 
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.ls colnam1 [string]
The column names in the first table used in the match.  If more than one
column is used, columns from the first and second
table are associated with each other based on their position in the list
and not on their names, i.e., the first column name in 'colnam1' is matched
to the first column name passed to 'colnam2', regardless of whether the
names match.
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.ls colnam2 [string]
The column names in the second table used in the match.  The same number of
column names must be passed to both the 'colnam1' and 'colnam2' parameters.
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EXAMPLES
1. There are two tables, "targets.tab", containing a list of targets
for observation, and "images.tab", containing a list of targets which
have already been observed.  Create a table named "new.tab" containing
those targets which have not previously been observed:

.nf
tt> tdiffer targets.tab images.tab new.tab targetid targetid
.fi
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BUGS
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REFERENCES
This task was written by Bernie Simon.
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SEE ALSO
tselect

Type "help tables opt=sys" for a higher-level description of the 'tables' 
package.
.endhelp
