Re: Arrays of Structures

["R.G. Stockwell" <stockwell(at)co-ra.comremove>]

Ben Tupper <tupper@seadas.bigelow.org> wrote in message
39511D37.96A7BF8B@seadas.bigelow.org">news:39511D37.96A7BF8B@seadas.bigelow.org...
> Jared wrote:
>
> > Ben,
> >
> > An array of anonymous structures can be made.  For example:
> >
> > a = replicate( {a:0, b:.1, c:''}, 10)
> >
> > makes a 10 element array of anonymous structures.  Hope this helps.
> >
> > Jared
>
> Thanks,
>
> Ah, that was easy!
>
> Now here's 'How come #2'
> I know that I can replace a given field in one of the structures.
> How come I can't replace Array element X with an identical structure (as
> I would with a named structure?)
>
>
> IDL> S1 =  {a:0, b:.1, c:''}
> IDL> S2 = {a:3, b:7., c:'x'}
> IDL> A = Replicate(S1,3)
> IDL> A(1).c = 'q'                 ;replace a field value without a
> problem
> IDL> A[1] = S2                    ; can't replace a structure.
> % Conflicting data structures: S2,A.
> % Execution halted at:  $MAIN$
>
> Thanks,
> Ben
>
> --
> Ben Tupper
>
> Bigelow Laboratory for Ocean Science
> tupper@seadas.bigelow.org
>
> pemaquidriver@tidewater.ne


Because they are not identical.  They are not the same "type" of
structure, where by "type" I mean they get different tags.
IDL>  help,s1,s2,/st
** Structure <1321598>, 3 tags, length=16, refs=2:
   A               INT              0
   B               FLOAT          0.100000
   C               STRING    ''
** Structure <13272f8>, 3 tags, length=16, refs=1:
   A               INT              3
   B               FLOAT           7.00000
   C               STRING    'x'

Here the names are different (<1321598> and  <13272f8>), so presumably IDL
does not know they are the same structure (I guess they don't do the
overhead of
parsing thorugh the structure to see if they really are the same).

Note that you can do the following (i.e. you can replace a structure element
if
it has the same tag):
; make the structure different
A.c ='bob'
print,a
A[1] = S1
print,a


Cheers.
bob