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Subchapters:

The structures

You can create a sub-array containing those stars:

      IDL> my_stars = catalog[index]
      IDL> help,my_stars
            MY_STARS        STRUCT    = -> ETOILE Array[33]

You can also sort your catalog according to one of the tags. Let's define first the index table of the sorted my_stars catalog, according to the magnitude:

      IDL> sort_index = sort(my_stars.mag)
      IDL> help,sort_index
            SORT_INDEX      LONG      = Array[33]

Like for the where condition, the returned index is not the sorted table, but the index of the elements. You can now print the sorted sub-catalog using a format similar to the Fortran one:

      IDL> print,my_stars(sort_index), $
      IDL>                     format='(a10,"  ra=",f7.3,"  dec=",f7.3,"  mag=",f 7.3)'
             etoile_15  ra= 30.015  dec= -0.752 mag= 10.722
             etoile_11  ra= 31.163  dec= -9.109  mag= 10.761
             etoile_16  ra= 39.789  dec= -7.716  mag= 11.071
             etoile_14  ra= 35.110  dec=  6.785  mag= 11.176
             etoile_31  ra= 33.530  dec=  9.306  mag= 11.823
             etoile_04  ra= 33.480  dec=  5.568  mag= 11.978
             etoile_00  ra= 31.795  dec=  7.631  mag= 12.055
             etoile_18  ra= 35.884  dec=  8.612  mag= 12.516
             etoile_17  ra= 38.860  dec=  2.498  mag= 12.628
             etoile_19  ra= 37.472  dec=  8.993  mag= 12.722
             etoile_12  ra= 36.151  dec=  7.670  mag= 12.792
             etoile_20  ra= 31.940  dec=  4.497  mag= 13.276

 

IDL courses C. Morisset 2004 IA/UNAM V 2.2

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