fsort -- Sort the contents of a FITS table


        fsort filename[ext#] column 


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.


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.


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



ftsort, fv, the interactive FITS file editor, can also be used to sort a FITS table.


Sept92 ftools.futils