FSORT (Sept92) ftools.futils FSORT (Sept92)
NAME
fsort -- Sort the contents of a FITS table
USAGE
fsort filename[ext#] column
DESCRIPTION
This task sorts the rows in a FITS table based on the values in a
specified column of the table. The table is sorted in place, so as
a precaution one should always save a copy of the table before
running this task. Aborting this task once it has started can
leave the FITS table in a corrupted state. The table may be sorted
in ascending or descending order, and multi-column sorting may also
be performed. The later means that once the rows have been sorted
on the value of the first column, then all identical values in the
first column will be sorted in order of the second specified
column, and so on.
PARAMETERS
infile [file name]
The file name (and extension number in square brackets) of the
FITS file to be sorted.
columns [string list]
A list of column names appearing in the FITS table extension to
be sorted in the order specified.
method = "heap" [string]
Sorting algorithm to be used. Currently supported algorithms
are the "heap"(NlogN) and "insert"(N**2) sort. The heap sort
gives the best speed when dealing with large random datasets.
The insertion sort works best when the dataset is very nearly
sorted, i.e., one value out of place.
(ascend = yes) [boolean, yes=ascend, no=descend]
An optional boolean flag used to determine if sorting is to be
done in ascending or descending order. This flag applies to all
columns sorted.
(unique = no) [boolean, yes=keep unique, no=keep all]
An optional boolean flag used to determine if rows with
identical sort keys should be purged, keeping one unique row.
Columns not included in the sort are not tested for uniqueness.
EXAMPLES
1. Sort the time column found in the second table extension in
ascending order in the FITS file test.fits
ft> fsort test.fits[2] time
2. Sort using the X and then the Y columns found in the first
extension in descending order in the FITS file test.fits, deleting
duplicate rows containing the same values of X and Y.
ft> fsort test.fits "X Y" ascend=no unique=yes
BUGS
SEE ALSO
ftsort, fv, the interactive FITS file editor, can also be used to
sort a FITS table.