Re: deleting structure element

[Alex Schuster <alex(at)pet.mpin-koeln.mpg.de>]

David Fanning wrote:

> > Bernard Puc (bpuc@va.aetc.com) writes:
> >
> > > Is there a neat, clever way to "delete" an element from a structure?

> On further (and more sober) reflection I would probably
> answer like this:
> 
> No way, no how, if you have a named structure. If you
> have an anonymous structure you *could* (under extreme
> duress) simply redefine the structure without the
> *&%%$^ field:
> 
>    struct = { a:0, b:0, c:0}
>    struct = { a:struct.a, b:struct.b }

I once wrote a routine for that purpose (attached). It replaces an
element (tag) of a structure by another element or deletes it. Which
doesn't work for the first element, well, if anyone wants to fix this...

    struct = { a:0, b:0, c:0
    replace_tag, struct, 'c', '' ; deletes tag c
or:
    replace_tag, struct, 'c', 'd', 100 ; replaces tag c with d (an int
with a value of 100)

        Alex
-- 
  Alex Schuster     Wonko@weird.cologne.de          PGP Key available
                    alex@pet.mpin-koeln.mpg.de
;+
; NAME:
;       REPLACE_TAG
;
; PURPOSE:
;       Replaces a tag in a structure by another
;
; CALLING:
;       replace_tag, struct, old_tag, new_tag, value
;
; INPUTS:
;	struct		- the structure to be changed
;	old_tag		- name of the tag to be changed
;	new_tag		- name of the new tag
;			  If set to '', old_tag is deleted from the structure
;	value		- value of the new tag
;
; RESTRICTIONS:
;	Does not work with named structures
;
; MODIFICATION HISTORY:
;       Alex Schuster, MPIfnF, 8/97 - Written
;-

pro replace_tag, struct, old_tag, new_tag, value

	tags = tag_names( struct )

	pos = (where( tags eq strupcase( old_tag ) ))(0)
	if ( pos eq -1L ) then begin
		print, 'Error: Tag ', old_tag, ' not in struct.' 
		return
	endif

	if ( ( pos eq 0 ) and ( new_tag ne '' ) ) then begin
		new_struct = create_struct( new_tag, value )
	endif else begin
		new_struct = create_struct( tags(0), struct.(0) )
		for i = 1, pos-1 do $
			new_struct = create_struct( new_struct, tags(i), struct.(i) )
		if ( new_tag ne '' ) then $
			new_struct = create_struct( new_struct, new_tag, value )
	endelse
	for i = pos+1, n_elements( tags )-1 do $
		new_struct = create_struct( new_struct, tags(i), struct.(i) )

	struct = new_struct

end