I have a list,

IDL> help, r
R               LIST  <ID=2  NELEMENTS=616>

composed of only a single type of object,

IDL> help, r[0]
<Expression>    OBJREF    = <ObjHeapVar3(RTSOLUTION)>
IDL> help, r[200]
<Expression>    OBJREF    = <ObjHeapVar1803(RTSOLUTION)>
..etc..

What I want to do is extract the same attribute from every object in the
list.

The way I'm doing it now is:

   radiance = DBLARR(r.Count())
   FOR i=0,r.count()-1 DO BEGIN
     r[i].get_property, radiance=x
     radiance[i]=x
   ENDFOR

and then I can do stuff with "radiance", such as plot it.

I find the above a little bit clunky since I have to explicitly iterate
through the list to pull out what I want, creating the temporary
"holding" array beforehand. If I want to extract more than one thing I
end up with something like

   n = r.Count()
   channel  = LONARR(n)
   radiance = DBLARR(n)
   FOR i=0,n-1 DO BEGIN
     r[i].get_property, radiance=x, channel=j
     radiance[i]= x
     channel[i] = j
   ENDFOR

which just looks messy.

Does anyone have any better/faster/more-elegant solutions to this sort
of problem?

I've had a look at the _overloadBracketsRightSide function documentation
but, to be honest, the description seems rather impenetrable to me. I
guess I'm looking for something akin to the "ELEMENTAL" attribute in
Fortran where a procedure written for in/output scalars can also operate
on any rank arrays (as long as they are conformable.)

cheers,

paulv

I created a new object that is just a list:

pro newObj__define
  compile_opt idl2

  _ = {newObj, $
    inherits list $
    }

Then, in my init, I created a struct like

function newObj::init, nSamples = nSamples
  compile_opt idl2

  newObjStruct = {newObjStruct, $
    radiance:0, $
    channel:0}

  self->add, replicate(newObjStruct, nSamples), /extract

  return, 1
end  

Then I overloaded the setProperty and getProperty functions.  

pro newObj::setProperty, _extra=extra
  compile_opt idl2

  if self->isEmpty() then return

  if (~n_elements(extra)) then return

  num = n_elements((tags=tag_names(extra)))

  lArray = self->toArray()
  self->remove, /all

  for ii=0, num-1 do begin
    ok = execute("lArray."+tags[ii]+ " = extra.(ii)")
  endfor

  self.add, lArray, /extract
end

pro newObj::getProperty, _ref_extra=extra
  compile_opt idl2

  if self->isEmpty() then return

  if (~n_elements(extra)) then return

  lArray = self.toArray()

  for ii=0, n_elements(extra)-1 do begin
    ok = execute("(scope_varfetch(extra[ii], /ref_extra)) = lArray."+extra[ii])
  endfor

end

http://idldatapoint.com/2012/01/05/a-technique-for-flexible-getsetpro...

The author did something similar to me, but uses a hash object inside his object, whereas I just inherited the list object into my object.

Thanks. I will have a closer look at your (and Mark's) technique.

In the meantime, what I came up with for my particular object is down
below. I reopened the List class to do it; a faux pas I know but...

-----%<-----
FUNCTION List::Get_Channel_Data, $
   data_name    , $ ; Input
   Debug = debug    ; Input keyword

   ; Set up
   @rtsolution_func_err_handler
   @rtsolution_parameters
   ; ...Check that *all* list members are RTSolution objects
   FOREACH element, self DO BEGIN
     IF ( ~ ISA(element,'RTSolution') ) THEN $
       MESSAGE, 'Non-RTSolution object found in channel list.', $
                NONAME=MsgSwitch, NOPRINT=MsgSwitch
   ENDFOREACH

   ; Construct the data retrieval command
   cmd_string = "self[i]->RTSolution::Get_Property, "+data_name+"=x"

   ; Define the return array
   n_channels = self.Count()
   data = MAKE_ARRAY(n_channels, VALUE = ZERO)

   ; Loop over list elements
   FOR i = 0L, n_channels-1 DO BEGIN
     ; ...Execute the command
     result = EXECUTE(cmd_string)
     IF ( result NE TRUE ) THEN $
       MESSAGE, "Error retrieving " + data_name + $
                " data for channel index " + STRTRIM(i,2), $
                NONAME=MsgSwitch, NOPRINT=MsgSwitch
     ; ...Save the channel data
     data[i] = x
   ENDFOR

   ; Done
   RETURN, data

END
-----%<-----

So once I've read my list-of-lists in

IDL> rtsolution_readfile, 'iasi616_metop-a.RTSolution.bin'
% RTSOLUTION_READFILE: Reading RTSolution profile #1
% RTSOLUTION_READFILE: Reading RTSolution profile #2
% RTSOLUTION_READFILE: Number of profiles/channels read from
iasi616_metop-a.RTSolution.bin : 2/616

I have my list of atmospheric profile results (the "profile" list),

IDL> help, rts
RTS             LIST  <ID=1  NELEMENTS=2>

each of which contains sensor spectral results (a "channel" list for
each "profile" entry),

IDL> help, rts[0]
<Expression>    LIST  <ID=2  NELEMENTS=616>

each of which contains the main object

IDL> help, (rts[0])[0]
<Expression>    OBJREF    = <ObjHeapVar3(RTSOLUTION)>

And now I can extract the same data from each object in the "channel" list:

IDL> help, rts[0].get_channel_data('radiance')
% Compiled module: LIST::GET_CHANNEL_DATA.
<Expression>    DOUBLE    = Array[616]
IDL> help, rts[1].get_channel_data('surface_emissivity')
<Expression>    DOUBLE    = Array[616]

etc..

Uff da. I really need to do more IDL metaprogramming.... :o)

cheers,

paulv

On 10/04/12 12:53, Paul Mallas wrote: